Bmal1 is a transcription factor that plays a central role in the regulation of circadian rhythms. Recent study reported that Bmal1-/- mice displayed many known features of premature ageing, such as reduction of bone mass. Our previous study has found that both the proliferation of bone marrow mesenchymal stem cells (BMSCs) and Bmal1 expression decreased with advancing age. It seemed that a positive correlation existed between Bmal1 protein level and the proliferative activity of BMSCs. β-catenin, the core factor of the canonical Wnt pathway, also showed reduced expression in aged mice. In order to further confirm this, we constructed a lentiviral vector to over-express Bmal1 in NIH-3T3 cells; successful transfection was verified. The cell proliferation rate of infected cells was higher than the non-transfected NIH-3T3 cells, suggesting that circadian clock gene Bmal1 can promote proliferation. β-catenin showed an increased expression in NIH-3T3 cells after Bmal1 over-expression, indicating that activation of the canonical Wnt pathway might be the mechanism underlying the effect of circadian clock gene Bmal on promoting cell proliferation.

Bone mesenchymal stem cell (BMSC) age-related changes include decreased osteogenesis and increased adipogenesis. Rev-erba and the Wnt/b-catenin signaling pathway were known to play important roles in BMSC aging. In this study, we have aimed to elucidate whether Rev-erba and Wnt/b-catenin signaling interact during BMSC proliferation and osteogenesis. Our results showed that Rev-erba expression gradually dropped during BMSC osteogenesis, and overexpression of Rev-erba in BMSCs inhibited cell proliferation and osteogenesis. The inhibition of cell proliferation induced by Rev-erba overexpression was partially reversed when Wnt/bcatenin signaling was activated. These results suggested that Rev-erba could promote BMSC aging and may be the negative regulator during the late stage of osteogenesis. The clock gene Rev-erba and Wnt/b-catenin signaling interact in the regulation of cell proliferation.