Cell-to-cell contact induces mesenchymal stem cell to differentiate into cardiomyocyte and smooth muscle cell

Background: Recent evidences have suggested that stem cell can differentiate into cardiomyocyte and smooth muscle cell (SMC) in vivo or in vitro. But the mechanism on how stem cell differentiates is still unknown. We investigated whether intercellular interaction or soluble chemical factors would induce mesenchymal stem cells (MSCs) to acquire the phenotypical characteristics of cardiomyocytes or SMC. Methods: MSCs were isolated from rat bone marrow with density gradient centrifugation and amplified in vitro. Flow cytometry was used to monitor the expression of surface antigen profile. After labeled by GFP (green fluorescent protein) transfection, rat MSCs were used to culture with adult rat cardiomyocytes and rat aortic SMCs in direct co-culture, indirect co-culture and conditioned culture, respectively. One week later, immunofluorescence staining against α-actin, desmin, and cardiac troponin T (cTnT) for cardiomyocyte, smooth muscle calponin and SM-α-actin for SMC were performed. Results: Immunofluorescence staining was positive against α-actin, desmin, and cTnT on MSCs in co-culture group with adult cardiomyocytes, positive against smooth muscle calponin and SM-α-actin on MSCs in co-culture group with SMCs. In contrast, no α-actin, desmin, and cTnT expression was observed in the indirect co-culture group and conditioned culture group; no smooth muscle calponin and SM-α-actin in the indirect co-culture group and conditioned culture group. Conclusions: Direct cell-to-cell contact between MSC and adult cardiomyocyte or SMC, but not the soluble signaling molecules is obligatory in the differentiation of MSC into cardiomyocytes or SMC.