Alterations in extracellular matrix quantity and composition contribute to atherosclerosis, with remodeling of the subendothelial basement membrane to a fibronectin-rich matrix preceding lesion development. Published data from our lab and others demonstrate that endothelial cell interactions with fibronectin prime inflammatory responses to a variety of atherogenic stimuli. However, the mechanisms regulating early atherogenic fibronectin accumulation remain unknown. Work from our group previously demonstrated that oxidized LDL (oxLDL) promotes endothelial proinflammatory gene expression by activating the integrin α5β1, a classic mediator of fibronectin fibrillogenesis. We now show that treating endothelial cells with oxLDL induces fibronectin deposition and inhibiting α5β1 (blocking antibodies, α5 knockout cells) completely inhibits oxLDL-induced fibronectin deposition. While endothelial fibronectin expression remains unchanged, oxLDL robustly stimulates the deposition of endothelial cell-derived fibronectin associated with a significant reduction in intracellular fibronectin. Interestingly, loss of endothelial cell-derived fibronectin, but not plasma fibronectin, prevents integrin α5 localization to focal adhesions, reduces fibronectin fibril length, and inhibits oxLDL-induced VCAM-1 expression. In addition, inducible endothelial-specific deletion of α5 integrins significantly blunts atherosclerotic plaque formation in ApoE knockout mice, suggesting an important role for this integrin in early endothelial activation. Taken together, our data demonstrate that oxLDL stimulates α5 integrin-dependent subendothelial matrix remodeling and endothelial proinflammatory gene expression through the deposition of fibronectin.
Defective catabolism of oxidized LDL by J774 murine macrophages.
