Laminar shear stress acts as a switch to regulate divergent functions of NF-κB in endothelial cells

Regions of the arterial tree exposed to laminar flow, which exerts high shear stress, are protected from inflammation, endothelial cell (EC) death and atherosclerosis. TNF alpha activates NF-kappa B transcription factors, which potentially exert dual functions by inducing both proinflammatory and cytoprotective transcripts. We assessed whether laminar shear stress protects EC by modulating NF-kappa B function. Human umbilical vein EC ( HUVEC) were cultured under shear stress (12 dynes/cm(2) for 16 h) using a parallel-plate flow chamber or were maintained in static conditions. Comparative real-time PCR revealed that preshearing significantly alters transcriptional responses to TNF alpha by enhancing the expression of cytoprotective molecules (Bcl-2, MnSOD, GADD45 beta, A1) and suppressing proinflammatory transcripts (E-selectin, VCAM-1, IL-8). We demonstrated using assays of nuclear localization, NF-kappa B subunit phosphorylation, DNA-binding, and transcriptional activity that NF-kappa B is activated by TNF alpha in presheared HUVEC. Furthermore, a specific inhibitor revealed that NF-kappa B is essential for the induction of cytoprotective transcripts in presheared EC. Finally, we observed that NF-kappa B can be activated in vascular endothelium exposed to laminar shear stress in NF-kappa B-luciferase reporter mice, thus validating our cell culture experiments. We conclude that shear stress primes EC for enhanced NF-alpha B-dependent cytoprotective responsiveness while attenuating proinflammatory activation. Thus modulation of NF-alpha B function may underlie the atheroprotective effects of laminar shear stress.