Interleukin-6-induced JAK2/STAT3 signaling pathway in endothelial cells is suppressed by hemodynamic flow

Endothelial cells (ECs) are constantly exposed to shear stress, the action of which triggers signaling pathways and cellular responses. During inflammation, cytokines such as IL-6 increase in plasma. In this study, we examined the effects of steady flow on IL-6-induced endothelial responses. ECs exposed to IL-6 exhibited STAT3 activation via phosphorylation of Tyr705. However, when ECs were subjected to shear stress, shear force-dependent suppression of IL-6-induced STAT3 phosphorylation was observed. IL-6 treatment increased the phosphorylation of JAK2, an upstream activator of STAT3. Consistently, shear stress significantly reduced IL-6-induced JAK2 activation. Pretreatment of ECs with an inhibitor of MEK1 did not alter this suppression by shear stress, indicating that extracellular signal-regulated kinase (ERK1/2) was not involved. However, pretreatment of ECs with an endothelial nitric oxide synthase inhibitor (nitro-L- arginine methyl ester) attenuated this inhibitory effect of shear stress on STAT3 phosphorylation. Shear stress-treated ECs displayed decreased nuclear transmigration of STAT3 and reduced STAT3 binding to DNA. Intriguingly, ECs exposed to IL-6 entered the cell cycle, as evidenced by increasing G(2)/M phase, and shear stress to these ECs significantly reduced IL-6-induced cell cycle progression. STAT3-mediated IL-6-induced cell cycle was confirmed by the inhibition of the cell cycle in ECs infected with adenovirus carrying the inactive mutant of STAT3. Our study clearly shows that shear stress exerts its inhibitory regulation by suppressing the IL-6-induced JAK2/STAT3 signaling pathway and thus inhibits IL-6-induced EC proliferation. This shear force-dependent inhibition of IL-6-induced JAK2/STAT3 activation provides new insights into the vasoprotective effects of steady flow on ECs against cytokine-induced responses.