Objective: To investigate the expression profiles of myocardin gene during the differentiation of bone marrow-derived mesenchymal stem cell to smooth muscle cells in the conditional medium combined with a high concentration of fetal bovine serum (FBS).
Methods: Marrow-derived mesenchymal stem cells were isolated and purified from mouse femoral bone and shinbones using differential adherent methods. Cells at the third passage were induced by 20% FBS in conditioned medium, conditioned medium alone, 20% FBS or 10% FBS alone respectively. Mouse aortic smooth muscle cells were cultured as the positive control. Levels of mRNA and protein expression of myocardin and several smooth muscle cells marker genes were determined by immunofluorescence, RT-PCR and Western blot before and 3, 7, 10, 14 d after the induction. The presence of smooth muscle myofilaments was detected by using transmission electron microscope.
Results: Naive bone marrow-derived mesenchymal stem cells displayed multiple morphological forms including fusiform, polygon, oval, and micro-spherical, as compared to the single macro-spindle form after the induction. Typical appearance of peak valley was displayed on the 21st day after induction. At the same time, the expression of smooth muscle marker genes was reinforced along with an up-regulation of myocardin expression. Immunofluorescence study showed that the cells expressing myocardin and smooth muscle marker genes such as alpha-SMA and SM-MHC increased. Fluorescence domain of myocardin translocated from cytoplasm to nucleus and the amounts of double positive cells for myocardin with alpha-SMA or SM-MHC also increased. RT-PCR confirmed that the mRNA expression of myocardin increased gradually and remained stabilized after achieving its peak on the 7th day after induction. The expression of smooth muscle marker genes, alpha-SMA and SM22alpha, remained stable on the 10th day of induction. It was also confirmed by Western blot that the protein expression of both myocardin and alpha-SMA were markedly increased during the induction. Finally, transmission electron microscopy revealed the presence of myofilament on the 21st day after induction.
Conclusions: Bone marrow-derived mesenchymal stem cells can be effectively induced into smooth muscle-like cells by conditioned medium combined with 20% FBS. Myocardin plays an important role in the differentiation process of bone marrow-derived mesenchymal stem cells to the peripheral smooth muscle cells.