Effects of stretched vascular endothelial cells and smooth muscle cells on differentiation of endothelial progenitor cellss

Differentiation of endothelial progenitor cells (EPCs) plays important roles in endothelial repair after vessel injury. Endothelial cells (ECs), vascular smooth muscle cells (VSMCs), and mechanical forces, including cyclic strain and shear stress, synergistically form the microenvironment of EPCs. However, the synergistic effect of cyclic strain, ECs, and VSMCs on the differentiation of EPCs remains unclear. In the present study, EPCs were indirectly co-cultured with stretched ECs or VSMCs that were subjected to 5%, 1.25-Hz cyclic strain by using FX-4000T Strain Unit. Then, Western blot and real-time PCR were used to examine expressions of EC marker, i.e., vascular cell adhesion molecule (VCAM), CD31, von Willebrand factor (vWF); VSMC markers, i.e., alpha-actin, Calponin, and SM22 alpha; and signaling molecules, i.e., p-Akt and p-ERK. In static, co-cultured ECs increased expression of VCAM and phosphorylation of Akt and ERK in EPCs compared to that in EPCs cultured alone. In EPCs, co-cultured VSMCs decreased expressions of CD31 and vWF, but increased expressions of Calponin and SM22 alpha. Stretched ECs reduced expressions of CD31 and vWF, enhanced Calponin and SM22 alpha, and repressed phosphorylations of Akt and ERK in EPCs. Stretched VSMCs decreased CD31, increased Calponin and SM22 alpha expressions, and repressed phosphorylation of Akt and ERK in EPCs. Our results suggest that ECs promoted EPC differentiation into ECs in static. VSMCs in static, as well as stretched ECs and stretched VSMCs, promoted EPC differentiation into VSMCs. Phosphorylation of Akt and ERK might be involved in EPC differentiation, mediated by the stretched ECs and VSMCs.