Mechanism of temporal gradients in shear-induced ERK1/2 activation and proliferation in endothelial cells

The aim of the current study was to investigate the intracellular signaling cascade that leads to temporal gradients in shear (TGS) induced endothelial cell proliferation, with a focus on the involvement of extracellular signal-regulated kinases 1 and 2 (ERK1/2). With the use of well-defined pulsatile, impulse, step, and ramp laminar flow profiles, we found that TGS (impulse flow and pulsatile flow) induced an enhanced and sustained (>30 min) phosphorylation of ERK1/2 relative to step flow (which contains a step increase in shear followed by steady shear), whereas steady shear (ramp flow) alone downregulated activated ERK1/2. Nitric oxide (NO) was found to mediate both the stimulatory effect of TGS and the inhibitory effect of steady shear on endothelial ERK1/2 phosphorylation. Reactive oxygen species (ROS) were also demonstrated to be associated with TGS-induced ERK1/2 phosphorylation. Both G(q/11) and G(i3) were necessary for the activation of ERK1/2 by TGS. Finally, the TGS-induced endothelial proliferative response was abolished by ERK1/2 inhibition. Our study demonstrated the essential role of G proteins, NO, and ROS in TGS-dependent ERK1/2 activation and proliferative response in vascular endothelial cells.