Effects of BMSCs interactions with adventitial fibroblasts in transdifferentiation and ultrastructure processes

In this study an in vitro model of simulated blood vessel injury was used to study the effects of bone marrow-derived mesenchymal stem cells (BMSCs) morphology and to detect vascular smooth muscle actin (SM α-actin) expression in the presence of adventitial fibroblasts. BMSCs from rats with DAPI-labeled nuclei were co-cultured with adventitial fibroblasts for 7 days, while BMSCs cultured alone served as controls. Cell morphology of BMSCs was assessed by laser confocal microscopy and SM α-actin or calponin expression in BMSCs was detected by immunofluorescence staining. The expression of SM α-actin mRNA was identified using RT-PCR. Cell ultrastructure was assessed by electron microscopy. The results demonstrate that BMSCs with DAPI-labeled nuclei were smaller compared with fibroblasts, and their nuclei emitted a blue fluorescence. Most BMSCs displayed a polygonal shape changing from their original long fusiform shape. BMSCs with blue nuclei and red cytoplasm (SM α-actin positive or calponin positive) were observed, and a substantial number of filaments were present in the cytoplasm as observed under electron microscopy. The number of these cells increased as a function of culture duration. However, SM α-actin expression was weak and calponin expression was not detected in the control group. This study provides important new information on the characterization of artherosclerosis pathogenesis and vascular restenosis after blood vessel injury. Our findings demonstrate that direct interactions with adventitial fibroblasts can induce vascular smooth muscle-like cell differentiation in BMSCs.