Junction-based lamellipodia drive endothelial cell rearrangements in vivo via a VE-cadherin-F-actin based oscillatory cell-cell interaction

Abstract

Angiogenesis and vascular remodeling are driven by extensive endothelial cell movements. Here, we present in vivo evidence that endothelial cell movements are associated with oscillating lamellipodia-like structures, which emerge from cell junctions in the direction of cell movements. High-resolution time-lapse imaging of these junction-based lamellipodia (JBL) shows dynamic and distinct deployment of junctional proteins, such as F-actin, VE-cadherin and ZO1, during JBL oscillations. Upon initiation, F-actin and VE-cadherin are broadly distributed within JBL, whereas ZO1 remains at cell junctions. Subsequently, a new junction is formed at the front of the JBL, which then merges with the proximal junction. Rac1 inhibition interferes with JBL oscillations and disrupts cell elongation—similar to a truncation in ve-cadherin preventing VE-cad/F-actin interaction. Taken together, our observations suggest an oscillating ratchet-like mechanism, which is used by endothelial cells to move over each other and thus provides the physical means for cell rearrangements.

Putting VE-cadherin into JAIL for junction remodeling

“…In mice and cell culture, elongated polarized cells display large JAIL that appear at the cell pole and are able to drive directed forward migration, whereas small JAIL at the lateral site allow for a relative displacement of adjacent cells. JAILmediated formation of new VE-cadherin adhesion sites has been recently confirmed in zebrafish, termed there 'junction-based lamellipodia' (Paatero et al, 2018), indicating that formation of JAIL is indeed a basic mechanism in angiogenesis. The iterative cycle between an interrupted VE-cadherin pattern and JAIL-mediated formation of new VE-cadherin adhesion sites continues until the Rel-VEcad-C has increased to the threshold (e.g.…”

“…In the endothelium, actin filaments exist within different structures: filament bundles, such as stress fibers and junction-associated actin filaments (JAAFs), filopodia, lamellipodia-like protrusions and the membrane cytoskeleton (for reviews, see Drenckhahn, 1982;Lampugnani, 2010;Marcos-Ramiro et al, 2014;Schnittler et al, 2014;Alon and van Buul, 2017;Schnoor et al, 2017a). Actin-driven membrane protrusions at EC junctions have been suggested to act as important regulators in cell junction dynamics (Hoelzle and Svitkina, 2012;Martinelli et al, 2013;Breslin et al, 2015;Belvitch et al, 2017;Paatero et al, 2018). JAIL develop as semicircular-shaped small (1 to 5 µm long) actin protrusions at cell junctions, which subsequently form new VE-cadherin adhesion sites and thus drive VE-cadherin dynamics .…”

“…Cell elongation increases cell border length and has been proposed to stimulate cell migration (Merks et al, 2006;Qutub and Popel, 2009;Cao et al, 2017), indicating that this effect is crucial. Indeed, cell elongation occurs in angiogenesis in vivo in the mouse retina and in zebrafish, and can also be induced in vitro by pro-angiogenic factors, such as VEGF and the γ-secretase inhibitor DAPT (Sauteur et al, 2014; Tsuji-Tamura and Ogawa, 2016; Cao et al, 2017;Paatero et al, 2018). The signals underlying cell elongation involve the loss of tension and microtubule polarization, as well as Rac, PI3K, Foxo1 and mTOR signaling (Furuyama et al, 2004;Tsuji-Tamura and Ogawa, 2016;Cao et al, 2017).…”

“…4A) (Cao et al, 2017). The mechanisms that lead to polarized cell migration in angiogenesis and sheet migration involve protrusive or repulsive and adhesive forces, which are mediated by actomyosin-mediated contraction, as well as formation of plasma membrane protrusions (Ballestrem et al, 2000;Waschke et al, 2004;Noda et al, 2010;Tambe et al, 2011;Yao et al, 2014;Bazellieres et al, 2015;Hayer et al, 2016;van Buul and Timmerman, 2016;Paatero et al, 2018).…”

Actin protrusions push on E-cadherin to maintain epithelial cell-cell adhesion

“…Protrusions are known to be important for initiating the formation of cell-cell adhesion (24, 25), More recently, protrusive activity was shown to be important for establishing and maintain cell-cell adhesion in endothelial cells (26–28). But epithelial cell-cell adhesion (7, 8, 29–31) is intrinsically more stable than that in endothelial cells (28, 32–34). Whether protrusive activity continues to operate in mature epithelial sheets is not known.…”