Abstract 131: Alphavbeta3 Integrins Mediate Shear Stress-Induced Inflammation and Early Atherogenesis

Rational 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. Signaling through transitional matrix binding integrins (α5β1, αvβ3 and αvβ5) drives shear stress-induced NF-κB activation and proinflammatory gene expression; however the specific contribution of each of these integrins remains unclear. Objective To address which transitional matrix-binding integrin mediates shear stress-induced endothelial cell. Methods and Results We now show that the small molecule αv integrin inhibitor S247, but not the α5 inhibitor ATN-161, abolished flow-induced proinflammatory signaling (PAK, NF-κB). Blocking αv expression using siRNA similarly prevents flow-induced activation of PAK and NF-κB, whereas siRNA-mediated knock-down of α5 did not. Furthermore, αv and β3 knockdown but not α5 and β5 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, indicating αvβ3 is the mediator for flow induced endothelial cell inflammation. 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. Lastly, inhibiting αv integrins using the small molecule inhibitor S247 reduces atherosclerotic plaque formation in ApoE knockout mice. Conclusion Taken together, these studies suggest that αvβ3 integrins mediate shear stress-induced proinflammatory responses associated with the transitional matrix in vitro and early atherosclerotic plaque formation in vivo .