The Role Of Low Shear Stress Induced Expression Of Receptor For Activated C Kinase1in Vascular Cells

Vascular remodeling induced by the variety of pathological factors is acommon pathogenesis and pathological process of many cardiovasculardiseases. Change of the hemodynamic shear stress, which is closelyassociated with atherosclerosis, plays an important role in vascularremodeling. Endothelial cells (ECs) are directly exposed to shear stress.Mechanical stimulus affects on vascular smooth muscle cells (VSMCs)via cellular signaling and cell-to-cell interaction. Studying the cross-talkbetween ECs and VSMCs, as well as the cell behavior under shear stress,contributes to the elucidation of the mechanobiological mechanism ofvascular remodeling.In our previous proteomics study, the differential protein profiles ofvascular tissue cultured under normal shear stress (NSS,15dyn/cm2) andLowSS (5dyn/cm2) ex vivo for24h were compared. Contrastively,activated C kinase1(RACK1) showed high expression under LowSS invascular tissue, suggesting that RACK1may participate in the LowSSinduced vascular remodeling.Through the application of ECs/VSMCs co-culture in the flowchamber system, we obtained the protein expression of RACK1and thephosphorylation level of Akt with the ECs and VSMCs that contact toeach other under the condition of static, NSS or LowSS. Meanwhile, in order to test whether direct contact or paracrine induced the regulation ofRACK1expression and Akt phosphorylation, we designed theECs//VSMCs separate culture model and obtained the same data as above.In addition, we also detected the apoptosis and Akt phosphorylation aftersuppressing the RACK1expression in VSMCs by using RNAinterference (RNAi) under static condition.The results showed that shear stress and co-cultured VSMCs had nosignificant effect on RACK1expression in ECs. RACK1was increasedunder LowSS in VSMCs by direct contacted with ECs. However,RACK1was repressed under both NSS and LowSS in VSMCs byparacrine. In ECs, NSS and LowSS inhibited Akt phosphorylation whichwas promoted under NSS in VSMCs by paracrine. Otherwise,suppressing the expression of RACK1downregulated the apoptosis andcaspase-3expression of VSMCs, but enhanced the phosphorylation ofAkt in VSMCs.Our results demonstrated that compared with NSS, LowSS conferredstronger inducement of RACK1expression in VSMCs via direct contactwith ECs. The opposite responses of shear stress in ECs or VSMCsshowed that NSS had more inhibition of Akt phosphorylation in ECs, butmore promotion in VSMCs. Our finding indicates that contact andinteraction between ECs and VSMCs possibly play an important role inmaintaining normal function of vascular cells and protecting structure ofvascular wall. Induced by cell contact and shear stress, RACK1mayinvolve in regulation of apoptosis through PI3K/Akt pathway.