The effect of flow on the expression of vascular adhesion molecule-1 by cultured mouse endothelial cells

Adherence of leukocytes to vascular endothelial cells (ECs) is known to be sensitive both to blood flow and adhesive proteins on EC surface. To elucidate the effect of blood flow on the surface expression of adhesive proteins, cultured ECs derived from mouse lymph nodes were exposed to different levels of wall shear stress in a flow-loading chamber, and changes in the expression of vascular adhesion molecule-1 (VCAM-1) and CD44 were evaluated by immunostaining with monoclonal antibodies and flow cytometry. Both proteins were expressed on non-activated cultured ECs. When exposed to flow with shear stress of 1.5 dynes/cm2 for 24 hr, VCAM-1 nearly disappeared on fluorescence micrographs, while CD44 showed no change. Flow cytometric analysis showed that the mean channel fluorescence of VCAM-1 was decreased about 75% by application of flow for 24 hr (p < 0.001), but that of CD44 remained unchanged. VCAM-1 expression began to decrease around 1 hr after the initiation of flow and became markedly reduced with time, reaching a minimum after 24 hr. When the cells subjected to flow for 24 hr were returned to stationary state, the reduced VCAM-1 expression was almost completely restored in 72 hr, indicating that the change was reversible. The magnitude of the reduction of VCAM-1 expression was also dependent on the intensity of the wall shear stress applied, ranging from 0 to 7.2 dynes/cm2. These results, demonstrating an explicit down-regulating effect of flow on VCAM-1 expression of cultured ECs, suggested preferential adhesion of leukocytes to ECs at low shear regions at the vascular wall.