Effect And Mechanism Of Flow Shear Stress On Migration And Proliferation Of Vascular Cells

Vascular remodeling is the adaptive changes on the vascular struture and function during organism growth, development, aging and disease. It had been well investagated that shear stress(SS)play critical roles in vascular remodeling, which are characterized as the disfunction of endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). However, the mechanism of vascular remodeling due to shear stress remains to be elucidated.Our previous comparative proteomic work showed that low shear stress (5 dyn/cm~2, LowSS) upregulated Rab28 expression in cultured rat aorta. In the present study, we firstly investigated the role of Rab28 in vascular cell migration under LowSS. Using a parallel-plate co-culture flow chamber system, LowSS and normal shear stress (15 dyn/cm~2, NSS) were applied respectively for 12 h, with the static cultured cells as control. The changes of protein expression of Rab28 and phospho-ERK were analyzed in VSMCs by Western blotting; VSMC migration was also examined with Transwell migration assay under shear stress. Rab28 was silenced in ECs and VSMCs by RNA interference (RNAi) technology to study the possible mechanism of shear stress mediated cell migration. Further more, we investigated the separate and synergistic effect of VSMCs and shear stress on EC proliferation in the following five groups: EC/O, EC//VSMC, EC/VSMC, EC/O+SS and EC/VSMC+SS. Proliferating cell nuclear antibody (PCNA) expression, reflective of cell proliferation ability, and phosphorylation of Akt, a signal molecule, were examined by Western blotting.The results showed that VSMC migration, Rab28 expression and ERK phosphorylation were significantly increased by LowSS in VSMCs. ERK phosphorylation was significantly increased by LowSS in ECs. Rab28 knockdown by RNAi significantly downregulated the migration of ECs and VSMCs, but had no effect on phosphorylation of ERK in the cells. VSMCs increased PCNA expression and Akt phosphorylation in both co-culture conditions with and without physical contact. The PCNA expression and Akt phosphorylation induced by VSMCs were reversed partly by NSS subjection. TGFβ1 neutralizing antibody decreased the PCNA expression and Akt phosphorylation in ECs, which were induced by VSMCs culture without physical contact .These results indicate that LowSS induces the migration of VSMCs co-cultured with ECs. VSMCs promotes EC proliferation through the direct contact and paracrine effect, in which transport protein Rab28 and signal molecule Akt may be involved. EC and VSMC proliferation and migration are downregulated by NSS, which suggest an atheroprotective factor to maintain homeostasis of vascular function.