Estradiol-induced RORα expression positively regulates osteoblast differentiation.

The retinoic acid receptor-related orphan receptor alpha (RORα) is a member of the nuclear hormone receptor superfamily. Several studies show that estradiol is related to RORα expression. However, the link between estradiol and RORα in osteoblast differentiation remains unknown. Here, we showed that estradiol induces RORα expression in C3H10T1/2 and MC3T3-E1 cells. RORα overexpression increased the expression of osteogenic genes including bone morphogenetic protein 2 (BMP2), distal-less homeobox 5, inhibitor of DNA binding, runt-related transcription factor 2 (Runx2), and osteocalcin. In addition, RORα increased phosphorylation of smad1/5/9. Furthermore, RORα knockdown suppressed estradiol-induced BMP2 and Runx2 protein level. Also, we confirmed that estradiol-induced ALP staining and matrix mineralization was attenuated in RORα knockdown. Summarily, these results suggest that estradiol-induced RORα promotes osteoblast differentiation.