Laminar shear stress suppresses vascular smooth muscle cell proliferation through nitric oxide-AMPK pathway

In healthy condition, vascular smooth muscle cells (VSMCs) are not directly exposed to shear stresses, because they are shielded by endothelial cell (EC) layer that lines blood vessels. After injury to EC layer caused by rupture of atherosclerotic lesions or invasive techniques such as angioplasty, VSMCs are directly exposed to blood flow which modulate molecular signaling and function. In endothelium, exposure to fluid shear stress has been reported to induce AMP-activated protein kinase (AMPK) phosphorylation and nitric oxide (NO) production. However, the influence of laminar shear stress on exposed VSMC is not defined. In this study, we investigated whether laminar shear stress regulates AMPK phosphorylation in VSMC and tried to identify underlying signaling pathway. NO production was increased by shear stress. The expression of NOS isoforms was increased 1 h after exposure to shear stress, and AMPK phosphorylation started to increase after 2 h. AMPK and LKB1, the upstream kinases of AMPK, phosphorylation were decreased by the non-selective NOS inhibitor l-NAME and the selective iNOS inhibitor aminoguanidine despite exposure to shear stress. On the other hand, compound C, a specific AMPK inhibitor, did not affect the expression of NOS isoforms. In addition, PDGF-induced VSMC proliferation was decreased by shear stress and restored by l-NAME. These findings suggest that shear stress upregulated AMPK phosphorylation in VSMC via NOS expression may be a beneficial route to prevent pathogenesis in the vascular system.