Chondrogenic differentiation of bovine bone marrow mesenchymal stem cells in pellet cultural system

Objective Pluripotent mesenchymal stem cells (MSC) have been isolated and well characterized from several tissue sources, including bone marrow stroma. MSC from different animals showed slight differences in morphology and in the potential to differentiate. In the present study, we isolated MSC from bovine bone marrow and induced chondrogenesis in order to establish a new experimental model of stem cell research. Methods Bone marrow was harvested from 8 calves. For inducing chondrogenesis, MSC were cultured in pellet culture system in a chemically defined medium supplemented with 0 and 10 ng/mL of transforming growth factor β1 (TGF-β1). Chondrogenic differentiation was evaluated by histological, immunohistochemical, and in situ hybridization techniques. The degrees of genes expression were measured by quantitative RT-PCR. Results Metachromatic alcian blue staining and immunoreactivity for type II collagen were detected in both pellet groups (0 and 10 ng/mL TGF-β1) after 7 days of culturing. In situ hybridization demonstrated strong expression of type II collagen and aggrecan mRNAs in the round cells located at the center region of pellets and at densely organized areas. On the other hand, type I collagen mRNA was strongly expressed in the superficial layer of the pellets. After 20 days of pellet culture, expression of type II collagen mRNA in the cells which were not treated by TGF-β1 was 1.7-fold higher compared with that treated by TGF-β1. Conclusion Independent, spontaneous chondrogenesis of bovine MSC in pellet culture occurred without addition of any external bioactive stimulators, namely factors from TGF-β family, which were previously considered necessary.