Background: Mesenchymal stem cells (MSCs) hold promise for application in adult stem cell-mediated regenerative medicine in bone remodeling and fracture repair. MSCs in vitro can be directed to osteogenic lineage by dexamethasone (DEX); however, the use of DEX is not practical in clinical settings because of adverse side effects such as glucocorticoid-induced osteoporosis. For identifying substances that facilitate osteogenesis, a monitoring system, which detects the osteogenic differentiation stage of MSCs accurately and easily, is required.
Methods: By focusing on the human osteocalcin (OC) gene whose expression profile is described along with osteogenic differentiation, we constructed the luciferase (Luc) reporter gene driven by the enhancer/promoter sequence of the human OC gene (OC-Luc) utilizing a mammalian artificial chromosome. Mammalian artificial chromosome is a suitable platform for loading reporter constructs, because of its stable episomal maintenance in host cells, transferability into any cell and assurance of long-term physiological transgene expression. We loaded the OC-Luc on a mammalian artificial chromosome vector engineered from mouse chromosome (designated as mouse artificial chromosome, MAC) in Chinese hamster ovary cells (OC-Luc/MAC) and transferred this into human MSC cells via chromosome transfer.
Results: OC-Luc/MAC in human MSC cells are responsive to positive and negative stimulation by 1 alpha,25-dihydroxyvitamin D3 and DEX in differentiation stage of MSCs to osteoblasts, reflecting the manner of physiological expression.
Conclusion: The OC-Luc/MAC reporter system may contribute not only to monitoring the osteogenic differentiation stage from MSC but also to identify novel osteogenic drugs.
Keywords: mammalian artificial chromosome; mesenchymal stem cells; osteocalcin; osteogenic differentiation; reporter assay.