α5β1 Integrin Signaling Mediates Oxidized Low-Density Lipoprotein–Induced Inflammation and Early Atherosclerosis

Abstract

Objective 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. The objective of our study was to determine whether endothelial matrix composition modulates the inflammatory properties of oxLDL. Approach and Results 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. Preventing α5β1 signaling (blocking antibodies, knockout cells) inhibits oxLDL-induced NF-κB activation and VCAM-1 expression. Furthermore, oxLDL-drives α5β1-dependent integrin signaling through the focal adhesion kinase (FAK) pathway and FAK inhibition (PF-573228, siRNA) blunts oxLDL-induced NF-κB activation, VCAM-1 expression, and monocyte adhesion. Lastly, treatment with the α5β1 signaling inhibitor, ATN-161, significantly blunts atherosclerotic plaque development in ApoE deficient mice, characterized by reduced VCAM-1 expression and macrophage accumulation without affecting fibrous cap size. Conclusions Our data suggest that α5β1-mediated crosstalk between fibronectin and oxidized LDL regulates inflammation in early atherogenesis and therapeutics that inhibit α5 integrins may reduce inflammation without adversely affecting plaque structure.

Activation of integrin α5 mediated by flow requires its translocation to membrane lipid rafts in vascular endothelial cells

“…6 B and D). These data demonstrate the importance of integrin α5 in atherogenesis in the Ldlr −/− mice, similar to that in Apolipoprotein E-deficient (Apoe −/− ) mice, reported by Yurdagul et al (16).…”

“…In our studies, we used the WD-fed Ldlr −/− model to test the role of integrin α5 in atherogenesis. The study by Yurdagul et al (16) also demonstrated the important role of integrin α5 activation for the atherogenic process using the Apoe −/− model; they found that α5 activation could also occur via a different mechanism that involved OxLDL (16). The fact that integrin α5 was demonstrated to play an obligatory role in atherogenesis in two different murine models (i.e., Ldlr −/− and Apoe −/− ), and can be activated by two different mechanisms (i.e., atheroprone flow and OxLDL), adds to the confidence that this pathway is highly relevant in vivo.…”

“…With respect to lipid rafts, clustering of ganglioside-abundant lipid rafts has been shown to regulate the activity of integrin β1 (15). Furthermore, a recent study by Yurdagul et al shows that integrin α5β1 is involved in OxLDL-induced activation of NF-κB in ECs (16). Although it is firmly established that activation of α5β1 mediates the NF-κB inflammatory axis in ECs, it is unknown whether a common molecular basis exists between the ability of atheroprone flow and OxLDL to activate integrin α5β1 and the subsequent molecular mechanisms by which α5β1 increases the inflammatory response, leading to atherosclerosis susceptibility.…”

αvβ3 Integrins Mediate Flow-Induced NF-κB Activation, Proinflammatory Gene Expression, and Early Atherogenic Inflammation

“…4,6 Cell culture models suggest that transitional matrix proteins enhance the endothelial proinflammatory response to multiple atherogenic risk factors, including both shear stress and oxidized low-density lipoprotein (oxLDL). 4,7 Transitional matrix proteins enhance shear stress-induced endothelial cell activation by promoting p21-activated kinase 2 (PAK2) signaling, which activates the transcription NF-kB to drive proinflammatory gene expression (ie, ICAM1 and VCAM1). 5,8 Limiting fibronectin deposition, either genetically or through peptide inhibitors, blunts endothelial proinflammatory signaling (PAK2, NF-kB) and gene expression both in models of acute disturbed flow-induced vascular inflammation (partial carotid ligation) and models of dietinduced spontaneous atherosclerosis.…”

“…5,8 Limiting fibronectin deposition, either genetically or through peptide inhibitors, blunts endothelial proinflammatory signaling (PAK2, NF-kB) and gene expression both in models of acute disturbed flow-induced vascular inflammation (partial carotid ligation) and models of dietinduced spontaneous atherosclerosis. 7,9,10 The integrin family of matrix receptors consists of 18 a and 8 b subunits that assemble into 24 different integrin heterodimers with distinct matrix-binding affinities and signaling properties. 11 Fluid shear stress activates multiple endothelial cell integrins, including the collagen-binding integrin a2b1 and the transitional matrix-binding integrins a5b1 and avb3.…”