Objective-Vascular endothelial cells (ECs) are subjected to shear stress and cytokine stimulation. We studied the interplay between shear stress and cytokine in modulating the expression of adhesion molecule genes in ECs. Methods and Results-Shear stress (20 dynes/cm2 ) was applied to ECs prior to and/or following the addition of tumor necrosis factor (TNF)-␣. Shear stress increased the TNF-␣-induced expression of intercellular adhesion molecule-1 (ICAM-1) at both mRNA and surface protein levels, but decreased the TNF-␣-induced expression of vascular adhesion molecule-1 (VCAM-1) and E-selectin. Transfection studies using promoter reporter gene constructs of ICAM-1, VCAM-1, and E-selectin demonstrated that these shear stress modulations of gene expression occur at the transcriptional levels. After 24-hour preshearing followed by 1 hour of static incubation, the effect of preshearing on TNF-␣-induced ICAM-1 mRNA expression vanished. The recovery of the TNF-␣-induced VCAM-1 and E-selectin mRNA expressions following preshearing, however, required a static incubation time of Ͼ6 hours (complete recovery at 24 hours). Pre-and postshearing caused a reduction in the nuclear factor-B-DNA binding activity induced by TNF-␣ in the EC nucleus. V ascular endothelial cells (ECs) are constantly exposed to fluid shear stress, a tangential force generated by the velocity gradient in viscous fluid flow. The nature and magnitude of shear stress play a significant role in the homeostasis of the structure and function of the blood vessel. Recent evidence suggests that physiological levels of laminar shear stress modulate cellular signaling and EC function and are protective against atherogenesis. 1 In human carotid and coronary arteries, atherosclerotic plaques are found in the vicinity of arterial bifurcations and bends, where the local flow is disturbed. 2 In contrast, regions of artery that experience laminar non-oscillatory shear stress were protected from atherosclerosis. The cytokine tumor necrosis factor-␣ (TNF-␣) is an important mediator of the inflammatory processes that occur during the progression of atherosclerosis. 3 Produced by macrophages that infiltrate the lesion, cytokines such as TNF-␣ are known to induce the expression of many endothelial genes that contribute to the complex processes involved in atherogenesis. 3 Well know examples include the transcriptional regulation of various adhesion molecules, such as intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin. 3 In contrast to laminar shear stress, cytokines are generally considered to be proatherogenic factors. Conclusions-OurDespite the intensive studies on the effects of fluid shear stress on ECs, the interplay of shear stress and cytokines in modulating EC gene expression and function has not fully been clarified. It has been shown that physiological levels of laminar shear stress inhibit the apoptosis of ECs induced by TNF-␣ and H 2 O 2 . 4,5 This inhibitory effect of shear stress is mediated by signalin...

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The phenotype of smooth muscle cells (SMCs) plays an important role in vascular function in health and disease. We investigated the mechanism of modulation of SMC phenotype (from contractile to synthetic) induced by the synergistic action of a growth factor (platelet-derived growth factor, PDGF-BB) and a cytokine (interleukin, IL-1␤). Human aortic SMCs grown on polymerized collagen showed high expression levels of contractile markers (smooth muscle ␣-actin, myosin heavy chain, and calponin). These levels were not significantly affected by PDGF-BB and IL-1␤ individually, but decreased markedly after the combined usage of PDGF-BB and IL-1␤. PDGF͞IL-1␤ costimulation also induced a sustained phosphorylation of Akt and p70 ribosomal S6 kinase (p70S6K). The effects of PDGF͞IL-1␤ costimulation on contractile marker expression and Akt and p70S6K phosphorylation were blocked by the phosphatidylinositol 3-kinase inhibitors wortmannin and LY294002 and by adenovirus expressing a dominant-negative Akt, and they were mimicked by constitutively active Akt. -1ra), as well as a specific inhibitor of PDGFR-␤ phosphorylation (AG1295); these agents also eliminated the PDGF-BB͞IL-1␤-induced signaling and phenotypic modulation. PDGF-BB͞IL-1␤ inhibited the polymerized collagen-induced serum response factor DNA binding activity in the nucleus, and this effect was mediated by the PDGFR-␤͞IL-1R1 association and phosphatidylinositol 3-kinase͞Akt͞p70S6K pathway. Our findings provide insights into the mechanism of SMC phenotypic modulation from contractile to synthetic, e.g., in atherosclerosis. PDGF-BB͞ IL-1␤ induced a sustained phosphorylation of PDGF receptor (PDGFR)-␤ and its association with IL-1 receptor (IL-1R1). Such activation and association of receptors were blocked by a PDGFR-␤ neutralizing antibody (AF385), an IL-1R1 antagonist (ILsignal transduction ͉ smooth muscle phenotype ͉ Akt ͉ mTOR