Fibronectin Matrix Assembly Regulates Shear Stress-Induced Structural Remodeling and Motility

Abstract

Complex spatial profiles of shear stress have been implicated in focal development of atherosclerotic lesions by mechanisms involving force transmission through endothelial cell (EC) focal adhesions to cytoskeleton. Fibronectin is a primary component of the provisional extracellular matrix (ECM) deposited in atherosclerotic lesions. Integrin-mediated mechanosignaling pathways in ECs are required for both adaptation to shear stress and fibronectin fibrillogenesis, but how fibronectin assembly state modulates EC responses to shear stress remains unknown. To investigate this question, focal adhesion displacement, cytoskeletal reorganization, and migration were measured before and after a step increase from 0 to 12 dyn/cm2 steady unidirectional shear stress acting on ECs interacting with either assembled, fibrillar fibronectin matrix or unassembled, fragmented fibronectin on glass. Shear stress onset induced the arrest of focal adhesion displacement in ECs on unassembled fibronectin but not in cells on assembled fibronectin. In subconfluent layers, ECs on unassembled fibronectin migrated downstream after shear stress onset, but cells on assembled fibronectin migrated in random directions associated with local fibril orientations. In confluent monolayers, ECs interacting with unassembled fibronectin aligned in the flow direction faster than in monolayers on fibrillar fibronectin matrix, suggesting that fibronectin assembly regulated shear stress-induced cytoskeletal remodeling. Since cytoskeletal remodeling and focal adhesion displacement reflect early mechanosensing events after the onset of shear stress, these data suggest that fibronectin assembly regulates mechanosensitivity at the cell-matrix interface, which leads to shear stress-induced adaptation of cell motility and alignment.