Role of retinoic acid-related orphan receptor-alpha in differentiation of human mesenchymal stem cells along with osteoblastic lineage.

OBJECTIVE

In a human mesenchymal stem cell (hMSC) model of osteoblast differentiation, we identified expression of the retinoic acid-related orphan receptor-alpha (RORalpha) gene as a candidate osteogenesis-related gene using gene expression profiling. RORalpha is a member of the nuclear receptor family of intracellular transcription factors and plays multifunctional roles in tissue development and differentiation, inflammation metabolism and circadian rhythms. However, the important role of RORalpha in the differentiation of hMSC along the osteoblastic lineage is not yet fully understood.

METHODS

To investigate the role of RORalpha during osteoblast differentiation, we eliminated RORalpha from hMSCs with a small interfering RNA molecule (siRNA), and investigated the effects of suppressing RORalpha by RT-PCR analysis.

RESULTS

We showed that suppressing the expression of RORalpha by the siRNA inhibited the expression of both bone sialoprotein and dentin matrix protein 1. It was discovered coincidentally that the inhibitory effect of RORalpha resulted in failure of mineralization and bone nodule formation during the course of osteogenesis.

CONCLUSION

The results of this study indicate that RORalpha must be an imperative modulator of bone sialoprotein and dentin matrix protein 1 involved in osteoblast differentiation and bone formation downstream of Wnt/beta-catenin signaling and just prior to the start of mineralization.