Endothelial FN (Fibronectin) Deposition by α5β1 Integrins Drives Atherogenic Inflammation

Objective Alterations in extracellular matrix quantity and composition contribute to atherosclerosis, with remodeling of the subendothelial basement membrane to an FN (fibronectin)-rich matrix preceding lesion development. Endothelial cell interactions with FN prime inflammatory responses to a variety of atherogenic stimuli; however, the mechanisms regulating early atherogenic FN accumulation remain unknown. We previously demonstrated that oxLDL (oxidized low-density lipoprotein) promotes endothelial proinflammatory gene expression by activating the integrin 51, a classic mediator of FN fibrillogenesis. Approach and Results We now show that oxLDL drives robust endothelial FN deposition and inhibiting 51 (blocking antibodies, 5 knockout cells) completely inhibits oxLDL-induced FN deposition. Consistent with this, inducible endothelial-specific 5 integrin deletion in ApoE knockout mice significantly reduces atherosclerotic plaque formation, associated with reduced early atherogenic inflammation. Unlike TGF (transforming growth factor )-induced FN deposition, oxLDL does not induce FN expression (mRNA, protein) or the endothelial-to-mesenchymal transition phenotype. In addition, we show that cell-derived and plasma-derived FN differentially affect endothelial function, with only cell-derived FN capable of supporting oxLDL-induced VCAM-1 (vascular cell adhesion molecule 1) expression, despite plasma FN deposition by oxLDL. The inclusion of alternative exon EIIIA (EDA) of FN (EIIIA) and alternative exon EIIIB (EDB) of FN (EIIIB) domains in cell-derived FN mediates this effect, as EIIIA/EIIIB knockout endothelial cells show diminished oxLDL-induced inflammation. Furthermore, our data suggest that EIIIA/EIIIB-positive cellular FN is required for maximal 51 recruitment to focal adhesions and FN fibrillogenesis. Conclusions Taken together, our data demonstrate that endothelial 5 integrins drive oxLDL-induced FN deposition and early atherogenic inflammation. Additionally, we show that 51-dependent endothelial FN deposition mediates oxLDL-dependent endothelial inflammation and FN fibrillogenesis.