Objective      To study the effect of direct contact with vascular smooth muscle cells on transdifferentiation of mesenchymal stem cells (MSCs).       Methods      Rat MSCs and vascular smooth muscle cells were cultured and identified

respectively. MSCs were labeled with DAPI firstly

and then co-cultivated with vascular smooth muscle cells for 3 or 5 d

or cultured with conditioned medium in which the vascular smooth muscle cells were in exponential phase of growth

or cultured alone as a control. The morphology of co-cultured cells were observed under light microscopy. Immunofluorescence was performed by using monoclonal antibodies against smooth muscle α-actin

calponin and CD31.       Results      The MSCs co-cultured with vascular smooth muscle cells expressed smooth muscle α-actin

calponin and CD31 at the third day of cultivation

and the positive cells increased at the fifth day. No cells positive for calponin and CD31 were detected when MSCs were cultured in conditioned medium or alone.       Conclusion      Cell-to-cell contact can induce rat MSCs to differentiate into vascular smooth muscle-like cells and endotheliocyte-like cells.