The role of BMP-6, IL-6, and BMP-4 in mesenchymal stem cell-dependent bone development: Effects on osteoblastic differentiation induced by parathyroid hormone and vitamin D3

Human bone marrow-derived mesenchymal stem cells (MSCs) represent an ideal source for cell therapy for inherited and degenerative diseases, bone and cartilage repair, and as target for gene therapy. The role of the combination of human parathyroid hormone (PTH) and vitamin D-3 in bone formation and mineralization has been established in several osteoblast cell culture studies. The aim of the present study was to evaluate the role of this hormonal combination alone and in the presence of bone morphogenetic protein-4 (BMP-4) or -6 (BMP-6) in inducing osteogenic differentiation of human MSC. Human MSC derived from adult normal bone marrow that are positive for CD29, CD44, CD105, and CD166 and negative for CD14, CD34, and CD45, were treated with the PTH and 1,25-dihydroxyvitamin D-3 in the presence and absence of recombinant human BMP-4 or BMP-6. PTH and vitamin D-3 induced high levels of expression of two key markers of bone formation: osteocalcin and alkaline phosphatase by MSCs. BMP-6 but not BMP-4 increased osteocalcin expression induced by PTH and vitamin D-3. Both BMPs enhanced calcium formation in MSC cultures and this response was potentiated by PTH and vitamin D-3. The present results revealed a novel potent effect of PTH and vitamin D-3 plus BMPs in inducing bone development by human MSCs. These results may facilitate therapeutic utility of MSCs for bone disease and help clarify mechanisms involved in stem cell-mediated bone development.