SIRT1 and Connexin40 Mediate the Normal Shear Stress-Induced Inhibition of the Proliferation of Endothelial Cells Co-Cultured with Vascular Smooth Muscle Cells

Background: Shear stress imposed by blood flow directly impacts endothelial cells (ECs), which are simultaneously influenced by neighboring vascular smooth muscle cells (VSMCs). However, the mechanisms by which shear stress and VSMCs modulate EC proliferation remain to be elucidated. Methods: ECs, cultured alone or co-cultured with VSMCs, were subjected to a normal level of laminar shear stress (NSS) of 15 dyne/cm2 or kept under static conditions by using a parallel-plate flow chamber system, respectively. Results: BrdU incorporation assay and flow cytometry revealed that NSS inhibited EC proliferation with or without VSMCs. Western blot analysis demonstrated that NSS down-regulated the expression of Connexin40 (Cx40) in both ECs cultured alone and ECs co-cultured with VSMCs, accompanied by the increased expression of SIRT1. Moreover, salermide, an inhibitor of SIRT1, as well as SIRT1-specifc siRNA transfection inhibited the effect of NSS on EC proliferation and Cx40 expression. In contrast, resveratrol, a SIRT1 activator, induced an alteration in ECs similar to the application of NSS. Conclusion: NSS inhibits the proliferation of ECs via SIRT1 and Cx40 in the presence or absence of VSMCs. The data suggest that NSS plays a protective role in vascular homeostasis by maintaining EC proliferation at a normal level