Crosstalk between reticular adherens junctions and platelet endothelial cell adhesion molecule-1 regulates endothelial barrier function.
OBJECTIVE
Endothelial cells provide a barrier between the blood and tissues, which is reduced during inflammation to allow selective passage of molecules and cells. Adherens junctions (AJ) play a central role in regulating this barrier. We aim to investigate the role of a distinctive 3-dimensional reticular network of AJ found in the endothelium.


RESULTS
In endothelial AJ, vascular endothelial-cadherin recruits the cytoplasmic proteins β-catenin and p120-catenin. β-catenin binds to α-catenin, which links AJ to actin filaments. AJ are usually described as linear structures along the actin-rich intercellular contacts. Here, we show that these AJ components can also be organized in reticular domains that contain low levels of actin. Reticular AJ are localized in areas where neighboring cells overlap and encompass the cell adhesion receptor platelet endothelial cell adhesion molecule-1 (PECAM-1). Superresolution microscopy revealed that PECAM-1 forms discrete structures distinct from and distributed along AJ, within the voids of reticular domains. Inflammatory tumor necrosis factor-α increases permeability by mechanisms that are independent of actomyosin-mediated tension and remain incompletely understood. Reticular AJ, but not actin-rich linear AJ, were disorganized by tumor necrosis factor-α. This correlated with PECAM-1 dispersal from cell borders. PECAM-1 inhibition with blocking antibodies or small interfering RNA specifically disrupted reticular AJ, leaving linear AJ intact. This disruption recapitulated typical tumor necrosis factor-α-induced alterations of barrier function, including increased β-catenin phosphorylation, without altering the actomyosin cytoskeleton.


CONCLUSIONS
We propose that reticular AJ act coordinately with PECAM-1 to maintain endothelial barrier function in regions of low actomyosin-mediated tension. Selective disruption of reticular AJ contributes to permeability increase in response to tumor necrosis factor-α.
Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain.
Laura
L
Fernández-Martín
Beatriz
B
Marcos-Ramiro
Carolina L
CL
Bigarella
Mariona
M
Graupera
Robert J
RJ
Cain
Natalia
N
Reglero-Real
Anaïs
A
Jiménez
Eva
E
Cernuda-Morollón
Isabel
I
Correas
Susan
S
Cox
Anne J
AJ
Ridley
Jaime
J
Millán
D022005:Adherens Junctions / Q000502:physiology*; D000577:Amides / Q000494:pharmacology; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000378:metabolism*; D051418:Focal Adhesion Kinase 2 / Q000502:physiology; D006801:Humans; D010539:Permeability; D010766:Phosphorylation; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000032:analysis / Q000502:physiology*; D011725:Pyridines / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D051176:beta Catenin / Q000378:metabolism
D000577:Amides; C495270:CTNNB1 protein, human; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D011725:Pyridines; D014409:Tumor Necrosis Factor-alpha; D051176:beta Catenin; C108830:Y 27632; D051418:Focal Adhesion Kinase 2