Dual role of vinculin in barrier-disruptive and barrier-enhancing endothelial cell responses

Endothelial cell (EC) barrier disruption induced by edemagenic agonists such as thrombin is a result of increased actomyosin contraction and enforcement of focal adhesions (FA) anchoring contracting stress fibers, which leads to cell retraction and force-induced disruption of cell junctions. In turn, EC barrier enhancement by oxidized phospholipids (OxPAPC) and other agonists is a result of increased tethering forces due to enforcement of the peripheral actin rim and enhancement of cell-cell adherens junction (AJ) complexes promoting EC barrier integrity. This study tested participation of the mechanosensitive adaptor, vinculin, which couples FA and AJ to actin cytoskeleton, in control of the EC permeability response to barrier disruptive (thrombin) and barrier enhancing (OxPAPC) stimulation. OxPAPC and thrombin induced different patterns of FA remodeling. Knockdown of vinculin attenuated both, OxPAPC-induced decrease and thrombin-induced increase in EC permeability. Thrombin stimulated the vinculin association with FA protein talin and suppressed the interaction with AJ protein, VE-cadherin. In contrast, OxPAPC stimulated the vinculin association with VE-cadherin. Thrombin and OxPAPC induced different levels of myosin light chain (MLC) phosphorylation and caused different patterns of intracellular phospho-MLC distribution. Thrombin-induced talin-vinculin and OxPAPC-induced VE-cadherin-vinculin association were abolished by myosin inhibitor blebbistatin. Expression of the vinculin mutant unable to interact with actin attenuated EC permeability changes and MLC phosphorylation caused by both, thrombin and OxPAPC. These data suggest that the specific vinculin interaction with FA or AJ in different contexts of agonist stimulation is defined by development of regional actyomyosin-based tension and participates in both, the barrier-disruptive and barrier-enhancing endothelial responses.