The Role Of SIRT1and SIRT6in The Function Change Of Vascular Cells In Response To Mechanical Stress

Vascular remodeling is an important process in initiation of manycardiovascular diseases. The mechanical stress plays a critical role invascular remodeling. Artery wall is exposed to three main kind ofhemodynamic stress, including shear stress, circumferential strain andnormal stress. Endothelial cells (ECs) and vascular smooth muscle cells(VSMCs) are the main cellular components in vascular wall. ECs areexposed to the blood flow and subjected to the shear stress directly andVSMCs locate in the media of arteries, which are affected by the cyclicstrain. The function change of them will result in or at least take part in thevascular remodeling; however, the mechanobiological mechanism ofvascular remodeling remains unclear to data. Sirtuin is a class of the NAD+dependent deacetylases. SIRT1and SIRT6are reported to have beneficialeffects on many diseases related with ages, including cardiovasculardiseases, diabetes II and cancer. However, there are rarely research aboutthe role of SIRT1and SIRT6in the mechanical stress modulating vascularcells.In part I of this thesis, ECs, cultured alone or co-cultured with VSMCs,were subjected to a normal level of laminar shear stress (NSS) of15 dyn/cm2or kept under static conditions by using a parallel-plate flowchamber system, respectively. BrdU incorporation assay and flowcytometry revealed that NSS inhibited EC proliferation with or withoutVSMCs. Western blot analysis demonstrated that NSS down-regulated theexpression of Connexin40(Cx40) in both ECs cultured alone and ECsco-cultured with VSMCs, accompanied by the increased expression ofSIRT1. Moreover, salermide, an inhibitor of SIRT1, as well asSIRT1-specific siRNA transfection inhibited the effects of NSS on ECproliferation and Cx40expression. In contrast, resveratrol, a SIRT1activator, induced an alteration in ECs similar to the application of NSS.NSS inhibits the proliferation of ECs via SIRT1and Cx40in the presenceor absence of VSMCs.In part II of this thesis, VSMCs were subjected to the cyclic strain byusing a Flexercell strain unit. It was demonstrated that the strain stimulatedVSMCs to secrete TGF-β1into the supernatant. After exposed to the strain,the expressions of contractile phenotype markers, including smooth muscleprotein22alpha, alpha-actin and calponin, and phosphorylated Smad2,phosphorylated Smad5, SIRT6and c-fos were up-regulated in VSMCs bywestern blot and immunofluorescence. In addition, the expression ofintercellular-adhesion molecule-1(ICAM-1) was also increased, which wasassayed with flow cytometry. The strained-induced up-regulation of SIRT6was blocked by a TGF-β1neutralizing antibody. Furthermore, the effects ofstrain on VSMCs were abrogated by SIRT6-specific siRNA transfection viathe suppression c-fos and ICAM-1. These results suggest that SIRT6mayplay a critical role in the regulation of VSMC differentiation into contractilephenotype in response to the cyclic strain.In conclusion, the physiological range of shear stress and cyclic strain inhibit the proliferation of ECs and promote VSMC differentiation intocontractile phenotype respectively in order to maintain vascular cells inhomeostasis, and SIRT1and SIRT6play a protective role for vascularstructure and function. These novel results highlight the mechanobiologymechanism in vascular remodeling.