Bone morphogenetic protein-2 regulates proliferation of human mesenchymal stem cells

Human mesenchymal stem cells obtained from the iliac crest of a single donor were investigated for cell proliferation, cell cycle profile, gene expression, and ultrastructural changes using electron microscopy. The human mesenchymal stem cells significantly increased their cell number by day 2 after treatment with bone morphogenetic protein-2 alone, or basic fibroblast growth factor alone or combinations of both proteins under serum-free conditions (p < 0.01). The human mesenchymal stem cells showed marked expression of cell nuclear antigen, notably at day 1, and pituitary tumor transforming gene throughout the experiment, suggesting cell cycle progression by bone morphogenetic protein-2 treatment. In addition, strong cellular nuclear bromodeoxyuridine incorporation was seen by immunocytochemistry. Fluorescence-activated cell sorting also showed a similar pattern of cell cycle progression with bone morphogenetic protein-2 treatment in serum-free medium and 10% fetal bovine serum treatment. The bone morphogenetic protein-2-treated human mesenchymal stem cells showed heterochromatin in the nucleus, suggesting cell differentiation, and well-developed granular endoplasmic reticulum, indicative of protein production. Overall, the human mesenchymal stem cells successfully proliferated with appropriate cell cycle progression and the cell ultrastructural morphology suggested marked nuclear and granular endoplasmic reticulum induction by bone morphogenetic protein-2 treatment in serum-free medium.