Abstract 306: Atheroprone Hemodynamics Regulate Smooth Muscle Cell Phenotype Through Endothelial PECAM and Fibronectin

Abstract

Introduction: Atherosclerosis is an inflammatory disease that develops preferentially in regions of disturbed hemodynamic shear stress. The extracellular matrix protein fibronectin (FN) is deposited in the sub-endothelial layer of pre-atherosclerotic and advanced lesions. Atheroprone shear stress promotes FN deposition and inflammatory signaling pathways in endothelial cells (ECs). Platelet endothelial cell adhesion molecule (PECAM), a mechanosensory protein, is necessary for the production, secretion, and assembly of FN matrix by ECs. Similar to ECs, vascular smooth muscle cells (SMCs) also display a pro-inflammatory phenotype in regions of atherogenesis, and this phenotype is key to the progression of atherosclerosis. Hypothesis: We hypothesize that endothelial PECAM and FN signaling promotes a pro-inflammatory smooth muscle cell phenotype in response to atheroprone shear stress patterns. Methods: An in vitro cone-and-plate viscometer model was used to apply human-derived atheroprone or atheroprotective shear stress patterns to human umbilical vein ECs co-cultured with underlying human umbilical vein SMCs. Results: Atheroprone flow increased SMC NFkB activity compared to atheroprotective flow (1.94±0.35 fold, p<0.05). This increase of SMC NFkB activity under atheroprone flow was attenuated by siRNA knockdown of either endothelial PECAM (0.56±0.08 fold, p<0.01) or FN (0.50±0.10 fold, p<0.01). Endothelial PECAM knockdown also reduced genes marking the SMC inflammatory phenotype, including smooth muscle alpha actin, vascular cell adhesion molecule 1, and cyclooxygenase-2. Conclusion: These results suggest that SMCs switch to a pro-inflammatory phenotype when overlying ECs are exposed to atheroprone shear stress, and that PECAM and FN signaling in the ECs regulate this phenotype.