The arterial microenvironment at atherosclerosis-prone sites primes the endothelium for activation by a variety of systemic atherogenic factors, in part through enhanced endothelial NF-?B expression at sites of disturbed flow. Additionally, disturbed flow patterns are permissive for subendothelial matrix remodeling, and work from my group and others have shown that fibronectin deposition enhances the endothelial proinflammatory response to both disturbed flow and oxidized LDL. Current research into the mechanisms of fibronectin deposition at atheroprone sites focus on altered fibronectin expression. However, our preliminary data show that oxidized LDL elicits robust fibronectin deposition driven by dynamic talin1-dependent integrin activation without altered fibronectin expression, suggesting a novel model for atherogenic matrix remodeling. In the previous grant period, we demonstrated that integrin-specific signaling differentially mediates flow and oxidized LDL induced NF-?B signaling and proinflammatory gene expression, and our published and preliminary data show that inhibiting or deleting endothelial fibronectin-binding integrins reduces early atherogenic inflammation in vivo. Despite the importance of integrin-mediated NF-?B activation in multiple systems, the signaling pathways linking integrins to NF-?B activation remain relatively unknown. The I?B kinase IKK? activates canonical NF-?B signaling, and both flow and oxLDL stimulate IKK?-dependent NF-?B activation. Nonproteolytic ubiquitination (K63-linked and Met1-linked ubiquitin chains) drives the formation of signaling microdomains that classically couple IKK? to its upstream activators through the recruitment of ubiquitin-binding proteins, such as obligatory IKK?-binding partner IKK?. Our preliminary data demonstrate robust K63 ubiquitination in integrin adhesion complexes associated with IKK? targeting, and blunting K63 ubiquitination prevents oxLDL-induced NF-?B activation. In addition, we show that endothelial cells lacking fibronectin-binding integrins display reduced responsiveness to proinflammatory stimuli, suggesting that integrin signaling contributes to endothelial priming associated with the atheroprone phenotype. The research outlined in this proposal will test the hypothesis that dynamic integrin activation in endothelial cells drives fibronectin deposition and integrin-specific signaling to promote endothelial activation. We will accomplish this by examining the mechanisms regulating talin1-dependent integrin activation and fibronectin deposition in vitro and in vivo using the endothelial talin1 L325R transgenic mice deficient for integrin activation (Aim 1). We will delineate the mechanisms regulating integrin-dependent nonproteolytic ubiquitination in IKK?/NF-?B activation and characterize how fibronectin-binding integrins prime the endothelial cells for activation (Aim 2). Lastly, we will utilize inducible endothelial-specific deletion models to determine whether endothelial fibronectin-binding integrins contribute to endothelial priming in vivo, to atherosclerotic plaque progression following early matrix remodeling, and to flow-induced arteriogenic inflammation (Aim 3).
Atherosclerosis, a chronic inflammatory disease of the vessel wall, is the leading cause of death in developed countries. Our research suggests that changes in the local extracellular matrix during atherosclerosis primes the tissue for inflammation. Normal components of the vascular matrix limit cellular responsiveness to transient injurious stimuli, while provisional matrix deposition in response to chronic stimuli enhances cellular responsiveness to propagate tissue remodeling. Understanding the molecular mechanisms by which matrix composition affects cell physiology could provide novel therapeutic targets to limit chronic inflammatory diseases, such as atherosclerosis and arthritis.
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