| Research Abstract |
In the downstream regions of stenotic vessels, cells are subjected to a vortex motion under low shear forces and atherosclerotic plaques tend to be localized. It has been reported that such a change of shear force on endothelial cells has an atherogenic effect by inducing the expression of adhesion molecules. However, the effect of vortex-induced mechanical stress on leukocytes has not been investigated. In this study, to elucidate whether vortex flow can affect the cell adhesive property, we have examined the effect of vortex-mediated mechanical stress on integrin activation in THP-1 cells, and its signaling mechanisms. When cells are subjected to vortexing at 400 to 2,000 rpm, integrin-dependent cell adhesion to vascular cell adhesion molecule-1 or fibronectin increased in a speed-and time-dependent manner. Next, to examine the role of Ca^<2+> this integrin activation, various pharmacological inhibitors involved in Ca^<2+> signaling were tested to inhibit the cell adhesion. Pretreatm
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ent of cells with BAPTA-AM, thapsigargin +NiCl_2, or U-73122 (a phospholipase C inhibitor) inhibited cell adhesion induced by vortex-mediated mechanical stress. We also found that W7 (a calmodulin inhibitor) blocked the cell adhesion. However, pretreatment of cells with GdCl_3, NiCl_2, or ryanodine did not affect the cell adhesion. These data indicate that vortex-mediated mechanical stress induces integrin activation through calmodulin and inositol-1,4,5 triphosphate-mediated Ca^<2+> releases from intracellular Ca^<2+> stores in THP-1cells. We also determined the effect of statins on vortex-induced integrin activation. Cells were pretreated with pravastatin or fluvastatin before vortex. Pretreatment of the cells with fluvastatin, but not pravastatin abrogated vortex-mediated cell adhesion to VCAM-1 and fibronectin, although both statins inhibited Rho activation by MCP-1. Fluvastatin dose-dependently inhibited vortex-induced cell adhesion from 10 to 50 μM. In summary, flow-mediated mechanical stress on THP-1 cells quickly induced β1 integrin activation via a calmodulin-mediated mechanism, and this integrin-mediated cell adhesion was blocked by fluvastatin. Thus mechanical stress-induced integrin activation in monocytes might explain increased atherosclerotic lesion formation in bifurcated or stenotic regions. These findings might enlighten a novel aspect of increased atherosclerosis at bifurcated and curved regions and anti-atherogenic effects of statins. Less
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