Abstract 483: Shear Stress-Induced Proinflammatory Responses on Transitional Matrices Require αv Integrins but Not α5β1

Abstract

The frictional shear stress generated by blood flow activates integrins on the endothelial cell surface, and signaling downstream of newly activated integrins regulates several flow-induced responses including inflammation and permeability. The extracellular matrix ligands for these integrins are altered early during atherosclerosis, as transitional matrix proteins such as fibronectin and fibrinogen accumulate in the subendothelial matrix. Signaling through transitional matrix binding integrins (α5β1, αvβ3 and αvβ5) drives shear stress-induced NF-κB activation and proinflammatory gene expression (ICAM-1, VCAM-1); however the specific contribution of each of these integrins remains unclear. We now show that α5 and αv expression occurs concomitant with early endothelial cell activation during atherosclerotic plaque formation in both mice and humans. Preventing αv integrin signaling (small molecule inhibitor S247, siRNA) abolished shear stress-induced proinflammatory signaling (p21-activated kinase (PAK), NF-κB), whereas preventing α5 integrin signaling (ATN-161, siRNA) did not. Furthermore, αv knockdown inhibited flow-induced ICAM-1 and VCAM-1 expression (both mRNA and protein) following either short term (5 hr) laminar and long term oscillatory (24 hr) shear stress. In contrast, αv knockdown did not affect TNFα-induced ICAM-1 and VCAM-1 expression, suggesting the anti-inflammatory effect of αv inhibition is specific to shear stress. Integrin inhibition did not affect all shear stress responses, as neither α5 nor αv siRNA affected shear stress-induced extracellular-signal regulated kinase (ERK1/2) activation. Taken together, these studies suggest that αv integrins (αvβ3, αvβ5) mediate shear stress-induced proinflammatory responses associated with the transitional matrix.