[Osteoblastic differentiation and in vivo osteogenic activity of marrow-derived mesenchymal stem cells stimulated by Tacrolimus: experiment with rats].

OBJECTIVE: To investigate the effect of the immunosuppressant Tacrolimus (FK506) on the osteoblastic differentiation and in vivo osteogenic inducement of bone marrow-derived mesenchymal stem cells (MSCs).

METHODS: MSCs were derived from Fischer 344 rats. Some MSCs were cultured with L-ascorbic acid-2-phosphate (AsAP) and beta-glycerophosphate (beta-GP) or FK506 plus AsAP and beta-GP. The alkaline phosphatase (APase) activity and calcium deposition were detected 4, 8, 12, and 16 days after the culture. Scanning electron microscopy was used to examine the calcified nodules. Northern blotting was used to detect the mRNA expression of osteocalcium. Multiparous beta-tricalcium phosphate (beta-TCP) ceramic cubes were dipped into 2 kinds of suspension of MSCs, treated by FK506 + AsAP + beta-GP or AsAP + beta-GP, so as to produce 48 pieces of MSCs/beta-TCP complex that were randomly divided into 2 equal groups to be cultured with AsAP + beta-GP or AsAP + beta-GP + FK506 for 4 weeks. The these pieces were transplanted into the subcutaneous sites of the rats' backs and were taken out 4 and 8 weeks later respectively for histological examination.

RESULTS: In vitro assays showed that the APase activity, calcium deposition, expression of osteocalcin mRNA of the FK506 + AsAP + beta-GP group at any time points were all significantly higher than those of the AsAP + beta-GP group (all P < 0.05). SEM showed that since the 16th day after culture calcified nodules began to be seen in the FK506 + AsAP + beta-GP group. Since the 4th weeks after transplantation remarkable new bone formation could be seen in the FK506 treated MSCs/beta-TCP complexes in comparison with those MSCs/beta-TCP complexes without treatment with FK506.

CONCLUSION: Greatly enhancing the in vitro osteoblastic differentiation and in vivo osteogenesis of MSCs, FK506 has a potential value as a bone growth factor and may improve the clinical result of bone transplantation used to treat large bone defect. The results of this experiment also contributes to a better understanding on the mechanism of immunosuppressants.