F-Actin–Anchored Focal Adhesions Distinguish Endothelial Phenotypes of Human Arteries and Veins

Abstract

Objective-Vascular endothelial-cadherin-and integrin-based cell adhesions are crucial for endothelial barrier function.Formation and disassembly of these adhesions controls endothelial remodeling during vascular repair, angiogenesis, and inflammation. In vitro studies indicate that vascular cytokines control adhesion through regulation of the actin cytoskeleton, but it remains unknown whether such regulation occurs in human vessels. We aimed to investigate regulation of the actin cytoskeleton and cell adhesions within the endothelium of human arteries and veins. Approach and Results-We used an ex vivo protocol for immunofluorescence in human vessels, allowing detailed en face microscopy of endothelial monolayers. We compared arteries and veins of the umbilical cord and mesenteric, epigastric, and breast tissues and find that the presence of central F-actin fibers distinguishes the endothelial phenotype of adult arteries from veins. F-actin in endothelium of adult veins as well as in umbilical vasculature predominantly localizes cortically at the cell boundaries. By contrast, prominent endothelial F-actin fibers in adult arteries anchor mostly to focal adhesions containing integrin-binding proteins paxillin and focal adhesion kinase and follow the orientation of the extracellular matrix protein fibronectin. Other arterial F-actin fibers end in vascular endothelial-cadherin-based endothelial focal adherens junctions. In vitro adhesion experiments on compliant substrates demonstrate that formation of focal adhesions is strongly induced by extracellular matrix rigidity, irrespective of arterial or venous origin of endothelial cells. Conclusions-Our data show that F-actin-anchored focal adhesions distinguish endothelial phenotypes of human arteries from veins. We conclude that the biomechanical properties of the vascular extracellular matrix determine this endothelial characteristic. (Arterioscler Thromb Vasc

Endothelial basement membrane laminin 511 is essential for shear stress response

“…However, few studies have examined FA in vivo (van Geemen et al , 2014). To investigate whether β1‐integrin‐containing FAs occur in the endothelium of resistance arteries and whether they change in the laminin knockout mice, en face staining of the endothelium in mesenteric resistance arteries for β1‐integrin together with vinculin as a marker of adhesion complexes (Collins et al , 2014; van Geemen et al , 2014) was performed, revealing localization of integrin β1 in adhesion complexes in the endothelium of WT, Lama4 −/− and Tek‐Cre::Lama5 −/− mice (Fig 4A). Quantification of the number and size of the vinculin‐positive adhesion complexes in the WT, Lama4 −/− and Tek‐Cre::Lama5 −/− mesenteric resistance arteries revealed significantly smaller but more numerous adhesion complexes in the Tek‐Cre::Lama5 −/− endothelium compared to WT littermates (Fig 4B–D).…”

Endothelium

“…van Geemen et al 2 bring convincing evidence that in vivo endothelial phenotype of human arteries and veins is determined by F-actin-anchored focal adhesion and biomechanical properties of extracellular matrix. In adult arteries, prominent F-actin fibers follow the orientation of fibronectin and anchor to focal adhesions recruiting integrin binding to paxillin and focal adhesion kinase, whereas in venous endothelium, F-actin fibers mostly localize cortically at cell boundaries.…”

Engulfed cadherin fingers are polarized junctional structures between collectively migrating endothelial cells

“…These serrated cell-cell junctions result from mechanical tension generated by actomyosin contractility 13,17 and have been observed in various endothelial in vitro systems as well as in ex vivo preparations of human endothelial tissues 18 .…”