Abstract 282: α5ß1 Integrin Signaling Through Focal Adhesion Kinase Mediates Oxidized LDL-Induced Endothelial Proinflammatory Gene Expression

Endothelial cell activation drives early atherosclerotic plaque formation. Both fibronectin deposition and accumulation of oxidized LDL (oxLDL) occur early during atherogenesis and both are implicated in enhanced endothelial cell activation. However, interplay between these responses has not been established. We now show that oxLDL-induced NF-κB activation, proinflammatory gene expression, and monocyte binding is significantly enhanced when endothelial cells are attached to fibronectin compared to basement membrane proteins. This enhanced response does not result from altered oxLDL receptor expression, oxLDL uptake, or reactive oxygen species production, but instead results from oxLDL-induced activation of the fibronectin-binding integrin α5β1. Correspondingly, oxLDL activates focal adhesion kinase (FAK), the downstream signaling partner to integrin α5β1. We also found enhanced integrin α5 expression and active FAK in the endothelium overlying atherosclerotic plaques in both mice and humans. Preventing α5β1 signaling (blocking antibodies, knockout cells) inhibits oxLDL-induced NF-κB activation and VCAM-1 expression. Also, inhibiting FAK kinase activity utilizing a small molecule inhibitor (PF-573228), siRNA, and kinase dead fibroblasts reduces oxLDL endothelial cell activation. Furthermore, treatment with the α5β1 signaling inhibitor, ATN-161, significantly blunts atherosclerotic plaque development in ApoE deficient mice, characterized by reduced macrophage accumulation without affecting fibrous cap size. Therefore, our data suggest that α5β1-mediated crosstalk between fibronectin and oxidized LDL regulates inflammation in early atherogenesis.