Atherosclerosis is an inflammatory disease of the arteries that develops preferentially in regions where shear stress, caused by blood flowing within the lumen of the vessel, is disturbed. Recent evidence demonstrates focal fibronectin (FN) expression in the subendothelial layer in pre-atherosclerotic and advanced lesions. We have found that atheroprone shear stress promotes FN deposition and inflammatory signaling pathways in endothelial cells (ECs). Recently, our lab discovered that EC

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... t endothelial cell adhesion molecule-1 (PECAM), which is important for sensing biomechanical stresses, is necessary for the production, secretion, and assembly of the FN-rich matrix in atheroprone regions. Similar to ECs, underlying vascular smooth muscle cells (SMCs) also display a proinflammatory phenotype in regions of atherogenesis, which is a key feature involved in the development of atherosclerosis. Our lab has designed a novel in vitro system that applies human-derived shear stresses to ECs, which are co-cultured with underlying SMCs. This allows for molecular manipulation of individual cell types, while permitting the study of the inherent signaling cross-talk between ECs and SMCs. Such an approach is useful because, while atheroprone shear stress is known to regulate EC signaling and promote a pro-inflammatory environment, the influence of that signaling on SMC phenotype has yet to be investigated. To assess the role of endothelial PECAM and FN signaling in promoting an inflammatory SMC phenotype, the co-culture model was exposed to atheroprone hemodynamic shear stress. siRNA knockdown of either PECAM or FN in ECs reduced SMC inflammatory genes, proteins, and transcription activity. The reduction in SMC inflammation also has the functional consequence of reducing monocyte adhesion. When EC FN is knocked down, the