Integrin Affinity Modulation Critically Regulates Atherogenic Endothelial Activation in vitro and in vivo

Abstract

While vital to platelet and leukocyte adhesion, the role of integrin affinity modulation in adherent cells remains controversial. In endothelial cells, atheroprone hemodynamics and oxidized lipoproteins drive an increase in the high affinity conformation of 5{beta}1 integrins in endothelial cells in vitro, and 5{beta}1 integrin inhibitors reduce proinflammatory endothelial activation to these stimuli in vitro and in vivo. However, the importance of 5{beta}1 integrin affinity modulation to endothelial phenotype remains unknown. We now show that endothelial cells (talin1 L325R) unable to induce high affinity integrins initially adhere and spread, but show significant defects in nascent adhesion formation. In contrast, overall focal adhesion number, area, and composition in stably adherent cells are similar between talin1 wildtype and talin1 L325R endothelial cells. However, talin1 L325R endothelial cells fail to induce high affinity 5{beta}1 integrins, fibronectin deposition, and proinflammatory responses to atheroprone hemodynamics and oxidized lipoproteins. Inducing the high affinity conformation of 5{beta}1 integrins in talin1 L325R cells partially restores fibronectin deposition, whereas NF-{kappa}B activation and maximal fibronectin deposition require both integrin activation and other integrin-independent signaling. In endothelial-specific talin1 L325R mice, atheroprone hemodynamics fail to promote inflammation and macrophage recruitment, demonstrating a vital role for integrin activation in regulating endothelial phenotype.