Although the BMPR-SMAD-RUNX2 signaling pathway plays widely recognized roles in BMP-induced osteogenesis, factors regulating this pathway remain to be defined. In this study, we used simulated microgravity models, which represent mechanical unloading conditions, to detect miRNAs that function in osteoblast differentiation. We found that miR-494 was persistently increased in C2C12 cells subjected to clinorotation conditions and in osteoblasts isolated from tail-suspended rats. Experiments showed that the overexpression of miR-494 correlated with a marked reduction in osteoblast differentiation genes and a decrease in osteogenesis in BMP2-induced osteogenetic differentiation. In contrast, the inhibition of miR-494 promoted BMP2-induced osteogenesis and partially rescued osteoblast differentiation disorder under simulated microgravity conditions. Mechanism studies revealed that miR-494 directly targeted BMPR2 and RUNX2, both of which play vital roles in the BMPR-SMAD-RUNX2 signaling pathway. More importantly, we demonstrated a positive feedback loop between miR-494 and MYOD, a critical transcription factor for myogenesis, indicating that miR-494 may participate in deciding cell fate of the multipotent mesenchymal stem cells (MSCs). Collectively, our study reveals an important role for miR-494 in regulating osteogenesis, the identification of which not only clarifies a regulator of BMP2-induced osteoblast differentiation, but also offers a possible strategy for preventing bone loss under microgravity conditions.
Keywords: BMP2; Osteoblast differentiation; Osteogenesis; Simulated microgravity; miRNA.