Endothelial cells dynamically compete for the tip cell position during angiogenic sprouting

Abstract

Sprouting angiogenesis requires the coordinated behaviour of endothelial cells, regulated by Notch and vascular endothelial growth factor receptor (VEGFR) signalling. Here, we use computational modelling and genetic mosaic sprouting assays in vitro and in vivo to investigate the regulation and dynamics of endothelial cells during tip cell selection. We find that endothelial cells compete for the tip cell position through relative levels of Vegfr1 and Vegfr2, demonstrating a biological role for differential Vegfr regulation in individual endothelial cells. Differential Vegfr levels affect tip selection only in the presence of a functional Notch system by modulating the expression of the ligand Dll4. Time-lapse microscopy imaging of mosaic sprouts identifies dynamic position shuffling of tip and stalk cells in vitro and in vivo, indicating that the VEGFR-Dll4-Notch signalling circuit is constantly re-evaluated as cells meet new neighbours. The regular exchange of the leading tip cell raises novel implications for the concept of guided angiogenic sprouting.

Inhibition of Notch signaling induces extensive intussusceptive neo-angiogenesis by recruitment of mononuclear cells

“…Recently, it has been shown that VEGFR1 and VEGFR2 reciprocally determine tip cell selection. For the initiation of the sprouting process, the cell needs lower VEGFR1 and higher VEGFR2 levels, where the latter is involved in negative feedback with Notch [4]. It is plausible to expect that with increase in the ratio VEGFR2/ VEGFR1, there will be enhanced sprouting.…”

“…Gerhardt et al demonstrated that during sprouting angiogenesis, endothelial cells compete for the leading tip position, and it is dependent not on the absolute but on the relative VEGFR levels between cells. The cells expressing less VEGFR1 or more VEGFR2 have high probability to be found at the tip position, and VEGFR level-mediated competition is strictly Notch dependent [4]. In addition to negative effects on sprouting, Notch signaling has also been shown to have effects on stabilization of vasculature and vessel remodeling [15][16][17][18][19].…”

“…Angiogenesis involves the formation of new blood vessels from a preexisting vascular plexus, and based on morphological characteristics, two distinct processes have been identified: sprouting angiogenesis and intussusceptive angiogenesis (IA) [1][2][3]. Sprouting angiogenesis has been well described in the recent literature and involves tip/stalk cell differentiation in the sprout and is tightly controlled by the Notch/Dll4 signaling pathway [4]. Intussusceptive angiogenesis is a specific mode of blood vessel formation by which instead of extraluminally, endothelial cells form intraluminal ''sprout like'' protrusions resulting in the formation of transluminal endothelial pillars.…”

Rab13-dependent Trafficking of RhoA Is Required for Directional Migration and Angiogenesis

“…Epithelial cells of Drosophila tracheal branches undergo extensive rearrangement (2), requiring remodeling of adherens junctions (3). Similarly, mural endothelial cells (ECs) 5 move extensively during intersegmental vessel (ISV) sprouting in the zebrafish (4,5), during the expansion of the retinal vasculature in the mouse, and during vessel sprouting from embryoid bodies (5). Junction remodeling between epithelial and ECs requires endocytosis and trafficking of junction transmembrane proteins (6).…”

L’angiogenèse tumorale

“…Chez l'adulte, mécanisme permet que seule la cellule de front, qui exprime fortement VEGF-R2 et la protéine DLL4, puisse répondre au signal pro-angiogénique induit par le VEGF. De manière intéressante, cette compétition de signalisation (DLL4 versus VEGF), et donc de positionnement de la cellule de front, pourrait assurer une sélection continue durant l'allongement du vaisseau et inté-grer d'autres signaux morphogénétiques tels que ceux induits par les BMP responsables de la quiescence des cellules [5]. SYNTHÈSE REVUES le modèle du poisson zèbre, l'analyse des vaisseaux intersomitiques montre que ces filopodes sont impliqués dans la vitesse de migration mais qu'ils ne participent pas à l'orientation de la cellule [7].…”