Endothelial Cell Differentiation by SOX17
2014; Lippincott Williams & Wilkins; Volume: 115; Issue: 2 Linguagem: Inglês
10.1161/circresaha.114.304234
ISSN1524-4571
AutoresJermaine Goveia, Annalisa Zecchin, Francisco Morales Rodriguez, Stijn Moens, Peter C. Stapor, Peter Carmeliet,
Tópico(s)Zebrafish Biomedical Research Applications
ResumoHomeCirculation ResearchVol. 115, No. 2Endothelial Cell Differentiation by SOX17 Free AccessEditorialPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessEditorialPDF/EPUBEndothelial Cell Differentiation by SOX17Promoting the Tip Cell or Stalking Its Neighbor Instead? Jermaine Goveia, Annalisa Zecchin, Francisco Morales Rodriguez, Stijn Moens, Peter Stapor and Peter Carmeliet Jermaine GoveiaJermaine Goveia From the Laboratory of Angiogenesis and Neurovascular link, Department of Oncology, University of Leuven, Leuven, Belgium (J.G., A.Z., F.M.R., S.M., P.S., P.C.); and Laboratory of Angiogenesis and Neurovascular link, Vesalius Research Center, VIB, Leuven, Belgium (J.G., A.Z., F.M., S.M., P.S., P.C.). , Annalisa ZecchinAnnalisa Zecchin From the Laboratory of Angiogenesis and Neurovascular link, Department of Oncology, University of Leuven, Leuven, Belgium (J.G., A.Z., F.M.R., S.M., P.S., P.C.); and Laboratory of Angiogenesis and Neurovascular link, Vesalius Research Center, VIB, Leuven, Belgium (J.G., A.Z., F.M., S.M., P.S., P.C.). , Francisco Morales RodriguezFrancisco Morales Rodriguez From the Laboratory of Angiogenesis and Neurovascular link, Department of Oncology, University of Leuven, Leuven, Belgium (J.G., A.Z., F.M.R., S.M., P.S., P.C.); and Laboratory of Angiogenesis and Neurovascular link, Vesalius Research Center, VIB, Leuven, Belgium (J.G., A.Z., F.M., S.M., P.S., P.C.). , Stijn MoensStijn Moens From the Laboratory of Angiogenesis and Neurovascular link, Department of Oncology, University of Leuven, Leuven, Belgium (J.G., A.Z., F.M.R., S.M., P.S., P.C.); and Laboratory of Angiogenesis and Neurovascular link, Vesalius Research Center, VIB, Leuven, Belgium (J.G., A.Z., F.M., S.M., P.S., P.C.). , Peter StaporPeter Stapor From the Laboratory of Angiogenesis and Neurovascular link, Department of Oncology, University of Leuven, Leuven, Belgium (J.G., A.Z., F.M.R., S.M., P.S., P.C.); and Laboratory of Angiogenesis and Neurovascular link, Vesalius Research Center, VIB, Leuven, Belgium (J.G., A.Z., F.M., S.M., P.S., P.C.). and Peter CarmelietPeter Carmeliet From the Laboratory of Angiogenesis and Neurovascular link, Department of Oncology, University of Leuven, Leuven, Belgium (J.G., A.Z., F.M.R., S.M., P.S., P.C.); and Laboratory of Angiogenesis and Neurovascular link, Vesalius Research Center, VIB, Leuven, Belgium (J.G., A.Z., F.M., S.M., P.S., P.C.). Originally published7 Jul 2014https://doi.org/10.1161/CIRCRESAHA.114.304234Circulation Research. 2014;115:205–207Vessel sprouting relies on the differentiation of endothelial cells (ECs) into a migratory tip cell leading at the forefront, proliferating stalk cells elongating the vessel stalk, and quiescent phalanx cells lining the perfused vessel.1 The tip versus stalk cell balance is under the control of vascular endothelial growth factor (VEGF) and Notch signaling, respectively.1 During recent years, the transcription factor SRY-related HMG box 17 (SOX17) has emerged as a regulator of arterial (at the expense of venous) EC specification, but its role in inducing the tip versus stalk EC behavior remained incompletely defined. In this issue of Circulation Research, Lee et al2 identified SOX17 as an inducer of the tip cell phenotype and showed that Notch signaling suppresses SOX17 levels to promote a stalk cell phenotype (Figure). However, using similar genetic mouse models, another recent study reported noncongruent findings.3 Can we explain these divergent interpretations and what are the possible implications of these results?Download figureDownload PowerPointFigure. Scheme illustrating the proposed models of the mechanism of Sox17 in vessel sprouting according to Lee et al.2 Sox17 plays a central role in the induction of tip cell differentiation. Expression of Sox17 in tip cells induces tip cell behavior, whereas Notch signaling downregulates Sox17 in endothelial cells to induce stalk cell specification. These results contradict with previous observations from Corada et al3 (discussed in insets) who report that Sox17 is a tip cell suppressor, upstream, not downstream, of Notch signaling. Red arrows indicate novel regulatory pathways dissected by Lee et al.2 Ang2 indicates angiopoietin-2; Dll4, Delta-like 4; ESM1, endothelial cell-specific molecule 1; NICD, Notch intracellular domain; and VEGFR2, vascular endothelial growth factor receptor 2. Article, see p 215Except for a brief period of embryonic vasculogenesis during which the primitive vascular plexus is established, tissues are vascularized by angiogenesis via formation of new vessel sprouts.4 VEGF and Notch are key orchestrators of the specification of ECs into migratory, sprout-guiding tip cells and proliferating, sprout-elongating stalk cells, respectively (Figure). VEGF, secreted by cells in response to hypoxia, induces tip cell formation and Delta-like 4 expression in ECs. Delta-like 4, a ligand of the Notch receptor, activates stalk cell–promoting Notch signaling in neighboring ECs to ensure that there is only a single tip cell followed by stalk cell neighbors.1 Intriguingly, tip and stalk cell phenotypes are fluidly interchangeable, and competition for the tip ensures that the most competitive EC leads the vessel sprout. Apart from VEGF and Notch, other genetic and even metabolic signals determine the tip versus stalk cell phenotype,1,5 but the nature of many of those signals still remains elusive. In this respect, the finding that SOX17 is a new signal orchestrating tip versus stalk cell behavior is exciting.Lee et al2 provide several lines of evidence that SOX17 induces tip cell function. First, they show SOX17 expression in ECs at the vascular front of angiogenic capillary plexuses, a finding that hints at a role in tip cell formation. Second, Sox17-silenced ECs have decreased expression of Delta-like 4, VEGF receptor 2, angiopoietin-2, Platelet derived growth factor B-B, and other genes associated with the tip cell phenotype. Third, silencing of Sox17 impairs EC migration, formation of lamellipodia, and other characteristic features of endothelial tip cells. Fourth, Sox17 deletion in ECs from embryonic day 8.5 in Tie2-Cre×Sox17GFP/fl mice results in lethal vessel defects. Furthermore, tamoxifen-induced deletion of Sox17 in ECs after birth in VE-cadherin-CreERT2×Sox17fl/fl mice reduced vascular plexus outgrowth, vessel branching, and tip cell formation. And finally, EC-specific Sox17 overexpression induced vascular hypersprouting in both embryonic and postnatal angiogenesis. Thus, Sox17 overexpression promotes ECs to adopt a tip cell phenotype, whereas conversely a lack of Sox17 promotes stalk cell differentiation.The SOX (SRY-related HMG box) family of proteins constitutes a group of 20 highly conserved transcription factors playing a pivotal role in the regulation of gene expression in various developmental processes. The group of SOX group F (SOXF) proteins, namely SOX7, SOX17 and SOX18, act in an overlapping manner to support the formation and integrity of the vascular system, as demonstrated by the severe cardiovascular defects displayed by knockout mouse embryos lacking either 1 (Sox7, Sox17) or 2 (Sox17 and Sox18) of these genes.6,7 The importance of SOX17 in inducing angiogenesis has also been highlighted in retinal and tumor angiogenesis.8,9 Interestingly, SOX transcription factors, including SOX17, interact with Notch signals to determine hemogenic and arterial specification of ECs.3,10 By using a combination of genetic and pharmacological loss- and gain-of-function approaches, Lee et al2 demonstrate that Notch suppresses SOX17 levels in ECs to promote a stalk cell phenotype.Although these exciting insights advance our understanding of the fundamental mechanisms of vessel sprouting, they also introduce another level of complexity in the proposed model of SOX17 vascular regulation. Another recent study by Corada et al3 reported that SOX17 is an upstream, not downstream, regulator of Notch signaling in arterial differentiation. Furthermore, this group observed a vascular hypersprouting, not hyposprouting, phenotype upon SOX17 deletion in ECs. How can these apparently contradictory findings be reconciled? Although the precise underlying causes remain to be identified, some hypothetical reasons are discussed. First, both groups used exactly the same genetically engineered knockout mouse models, thus excluding the possibility that a different sort of genetic manipulation caused the divergence. Nonetheless, slight alterations in genetic backgrounds of the transgenic models used could affect the phenotype.Second, the postnatal mouse retina model of angiogenesis is a dynamic model, and EC branching, plexus outgrowth, and arteriovenous differentiation occur in a short timeframe. Therefore, differences in tamoxifen administration schemes used by both groups (administration route, dose, and duration) possibly evoked differences in recombination efficiency and vessel remodeling dynamics. At least from a theoretical perspective, a deletion of a proangiogenic gene in only a fraction of ECs might initially impair vessel outgrowth, but resultant ischemia because of hypoperfusion might lead to vessel overgrowth by nonrecombined wild-type ECs in an effort to compensate for the vascular defect. Compensation by nontransgenic ECs has been previously shown to rescue vascular defects by mutant ECs with a competitive angiogenic disadvantage.11 Documenting the in situ recombination efficiency of ECs in a particular vascular bed might thus aid to understand the phenotype under investigation.Another discrepancy is the relationship between Notch and SOX17. Lee et al2 provide evidence that Notch signaling downregulates SOX17 expression at the post-transcriptional level to promote a stalk cell phenotype, whereas Corada et al3 report that Notch signaling is regulated by SOX17 (Figure). Although these divergent findings require further reconciliation, it is noteworthy that SOX transcription factor function is dependent on the formation of complexes with interacting partners. Thus, the type and level of activity of SOX factors might theoretically vary depending on the availability and the sort of its binding partners in distinct EC subtypes. Also, the levels of SOX17 might influence its association with additional or other types of partners. Nevertheless, beyond the apparent contradictions and contextual effects of SOX17, the findings by Lee et al2 and Corada et al3 seem to direct toward an intriguing model that defines SOX17 as an integral part of Notch signaling in the vascular biology governing EC specification.The findings by Lee et al2 and Corada et al3 also raise several outstanding questions. For instance, if SOX17 is a bona fide tip cell signal, is it then also capable of ensuring the competitiveness of ECs to reach the tip position in mosaic cell–cell competition assays in vitro and more importantly in vivo, as used in previous studies?12 SOX17 is preferentially expressed in arterial ECs, and silencing of SOX17 not only favors venous at the expense of arterial EC specification but also stimulates increased tip cell formation.3 Given that ECs are generally thought to sprout from veins, does this imply that deficiency of SOX17 then promote formation of tip cells after prior differentiation to venous subtypes? How are SOX17's context-dependent functions regulated, such as arterial differentiation and tip–stalk cell differentiation? Which other transcriptional cofactors are involved and how are they regulated? Which signals upregulate SOX17 levels in tip cells? How does the interplay between Notch and SOX17 affect the dynamic process of tip and stalk cell differentiation?Another outstanding question is whether SOX17 can become a target for angiogenic therapy and, if so, whether SOX17 should be blocked or activated to inhibit pathological angiogenesis. A previous study reported that EC-specific deficiency of SOX17 reduces vessel density while inducing vessel normalization in models of melanoma and lung cancer.8 These findings would lend support for the strategy to block SOX17 for inhibiting tumor angiogenesis. However, answering more conclusively the question whether SOX17 should be inhibited or stimulated to block pathological angiogenesis will require a better understanding of the contextual role of SOX17 in tip versus stalk cell–driven angiogenesis.Sources of FundingJ. Goveia is a PhD student supported by a Bijzonder onderzoeksfond (BOF) fellowship from the University of Leuven. S. Moens is supported by an Emmanuel Vanderschueren fellowship from the Flemish Association against Cancer (VLK). The work of P. Carmeliet is supported by a Federal Government Belgium grant (IUAP P7/03), long-term structural Methusalem funding by the Flemish Government, grants from the Research Foundation Flanders (FWO), the Foundation of Leducq Transatlantic Network (ARTEMIS), Foundation against cancer, an European Research Council (ERC) Advanced Research Grant (EU-ERC269073), and the AXA Research Fund.DisclosuresNone.FootnotesThe opinions expressed in this article are not necessarily those of the editors or of the American Heart Association.Correspondence to Peter Carmeliet, MD, PhD, Vesalius Research Center, VIB, KU Leuven, Campus Gasthuisberg, Herestraat 49-B912, Leuven B-3000, Belgium. E-mail [email protected]References1. Potente M, Gerhardt H, Carmeliet P. Basic and therapeutic aspects of angiogenesis.Cell. 2011; 146:873–887.CrossrefMedlineGoogle Scholar2. Lee SH, Lee S, Yang H, Song S, Kim K, Saunders TL, Yoon JK, Koh GY, Kim I. 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Lee J, Hur J, Kwon Y, Chae C, Choi J, Hwang I, Yun J, Kang J, Choi Y, Kim Y, Lee S, Lee C, Jo D, Seok H, Cho B, Baek S and Kim H (2021) KAI1(CD82) is a key molecule to control angiogenesis and switch angiogenic milieu to quiescent state, Journal of Hematology & Oncology, 10.1186/s13045-021-01147-6, 14:1, Online publication date: 1-Dec-2021. Southgate L, Machado R, Gräf S and Morrell N (2019) Molecular genetic framework underlying pulmonary arterial hypertension, Nature Reviews Cardiology, 10.1038/s41569-019-0242-x, 17:2, (85-95), Online publication date: 1-Feb-2020. Tao J, Han Q, Zhou H and Diao X (2019) Transcriptomic responses of regenerating earthworms (Eisenia foetida) to retinoic acid reveals the role of pluripotency genes, Chemosphere, 10.1016/j.chemosphere.2019.03.111, 226, (47-59), Online publication date: 1-Jul-2019. 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Iturriaga-Goyon E, Buentello-Volante B, Magaña-Guerrero F and Garfias Y (2021) Future Perspectives of Therapeutic, Diagnostic and Prognostic Aptamers in Eye Pathological Angiogenesis, Cells, 10.3390/cells10061455, 10:6, (1455) He Y, Tacconi C, Dieterich L, Kim J, Restivo G, Gousopoulos E, Lindenblatt N, Levesque M, Claassen M and Detmar M (2022) Novel Blood Vascular Endothelial Subtype-Specific Markers in Human Skin Unearthed by Single-Cell Transcriptomic Profiling, Cells, 10.3390/cells11071111, 11:7, (1111) July 7, 2014Vol 115, Issue 2 Advertisement Article InformationMetrics © 2014 American Heart Association, Inc.https://doi.org/10.1161/CIRCRESAHA.114.304234PMID: 24989487 Originally publishedJuly 7, 2014 KeywordsEditorialsreceptors, NotchPDF download Advertisement SubjectsAngiogenesisDevelopmental BiologyVascular Biology
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