Induction of Mineralized Nodule Formation in Rat Bone Marrow Stromal Cell Cultures by Silk Fibroin

Background: Silk fibroin is a suitable protein for osteogenesis by inducing markers of bone formation in the cultures of osteoblasts, so we examined the ability of this protein to induce mineralized nodules in the rat bone marrow stromal cell cultures. Methods: Bone marrow stromal cells obtained from 4 to 6 weeks old Spruge-Dawely male rats were grown in primary culture for seven days and then subcultured for 21 days. The secondary cultures were done on either silk fibroin-coated polystyrene plates or free-silk fibroin ones. After 21 days of grow up, the cultures were examined for nodule formation by scanning electron microscopy, for mineralization by alizarin red S staining and for expression of gene markers of osteoblast maturation by reverse transcription PCR (RT-PCR).  Results: The stromal cells were observed to form three-dimensional nodules when cultured on the silk fibroin and compared to the stromal cells cultured on the free-silk fibroin polystyrene plates, where no nodules were observed in the time-frame studied. These nodules were also found to be mineralized and expressed the gene markers of osteoblast. Conclusion: Silk fibroin could serve as suitable inducing factor by stimulating stromal cell differentiation to form mineralized nodules.