Fluid shear stress inhibits TNF-alpha activation of JNK but not ERK1/2 or p38 in human umbilical vein endothelial cells: Inhibitory crosstalk among MAPK family members

Atherosclerosis preferentially occurs in areas of turbulent flow and low fl uid shear stress, whereas laminar flow and high shear stress are atheroprot ective, Inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-al pha) and IL-1 stimulate expression of endothelial cell (EC) genes that may promote atherosclerosis. TNF-alpha and IL-1 regulate gene expression in ECs , in part, by stimulating mitogen-activated protein kinases (MAPK), which p hosphorylate transcription factors. We hypothesized that steady laminar flo w inhibits cytokine-mediated activation of MAPK in EC. To test this hypothe sis, we determined the effects of flow (shear stress = 12 dynes/cm(2)) on T NF-alpha and IL-1-stimulated activity of three MAPK in human umbilical vein ECs (HUVEC): extracellular signal-regulated kinase (ERK1/2), p38, and c-Ju n N-terminal kinase (JNK). Flow alone stimulated ERK1/2 and p38 activity bu t decreased JNK activity compared with static controls. TNF-alpha or IL-1 a lone activated ERK1/2, p38, and JNK maximally at 15 min in HUVEC. Preexposi ng HUVEC for 10 min to flow inhibited TNF-alpha and IL-1 activation of JNK by 46% and 49%, respectively, but had no significant effect on ERK1/2 or p3 8 activation. Incubation of HUVEC with PD98059, which inhibits flow-mediate d ERK1/2 activation, prevented flow from inhibiting cytokine activation of JNK. Phorbol 12-myristate 13-acetate, which strongly activates ERK1/2, also inhibited TNF-alpha activation of JNK. These findings indicate that fluid shear stress inhibits TNF-alpha -mediated signaling events in HUVEC via the activation of the ERK1/2 signaling pathway. Inhibition of TNF-alpha signal transduction represents a mechanism by which steady laminar flow may exert atheroprotective effects on the endothelium.