Stiff Substrates Increase Inflammation-Induced Endothelial Monolayer Tension and Permeability

Arterial stiffness and inflammation are associated with atherosclerosis, and each have individually been shown to increase endothelial monolayer tension and permeability. The objective of this study was to determine if substrate stiffness enhanced endothelial monolayer tension and permeability in response to inflammatory cytokines. Porcine aortic endothelial cells were cultured at confluence on polyacrylamide gels of varying stiffness and treated with either tumor necrosis factor-alpha (TNF alpha) or thrombin. Monolayer tension was measured through vinculin localization at the cell membrane, traction force microscopy, and phosphorylated myosin light chain quantity and actin fiber colocalization. Cell permeability was measured by cell-cell junction confocal microscopy and a dextran permeability assay. When treated with TNF alpha or thrombin, endothelial monolayers on stiffer substrates showed increased traction forces, vinculin at the cell membrane, and vinculin phosphorylation, suggesting elevated monolayer tension. Interestingly, VE-cadherin shifted toward a smaller molecular weight in endothelial monolayers on softer substrates, which may relate to increased VE-cadherin endocytosis and degradation. Phosphorylated myosin light chain colocalization with actin stress fibers increased in endothelial monolayers treated with TNF alpha or thrombin on stiffer substrates, indicating elevated cell monolayer contractility. Endothelial monolayers also developed focal adherens intercellular junctions and became more permeable when cultured on stiffer substrates in the presence of the inflammatory cytokines. Whereas each of these effects was likely mitigated by Rho/ROCK, Rho/ROCK pathway inhibition via Y27632 disrupted cell-cell junction morphology, showing that cell contractility is required to maintain adherens junction integrity. These data suggest that stiff substrates change intercellular junction protein localization and degradation, which may counteract the inflammation-induced increase in endothelial monolayer tension and thereby moderate inflammation-induced junction loss and associated endothelial monolayer permeability on stiffer substrates.