Laminar shear stress acts as a switch to regulate divergent functions of NF-kappaB 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. TNFalpha activates NF-kappaB 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-kappaB function. Human umbilical vein EC (HUVEC) were cultured under shear stress (12 dynes/cm2 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 TNFalpha by enhancing the expression of cytoprotective molecules (Bcl-2, MnSOD, GADD45beta, A1) and suppressing proinflammatory transcripts (E-selectin, VCAM-1, IL-8). We demonstrated using assays of nuclear localization, NF-kappaB subunit phosphorylation, DNA-binding, and transcriptional activity that NF-kappaB is activated by TNFalpha in presheared HUVEC. Furthermore, a specific inhibitor revealed that NF-kappaB is essential for the induction of cytoprotective transcripts in presheared EC. Finally, we observed that NF-kappaB can be activated in vascular endothelium exposed to laminar shear stress in NF-kappaB-luciferase reporter mice, thus validating our cell culture experiments. We conclude that shear stress primes EC for enhanced NF-kappaB-dependent cytoprotective responsiveness while attenuating proinflammatory activation. Thus modulation of NF-kappaB function may underlie the atheroprotective effects of laminar shear stress.