Chrysophanol increases osteoblast differentiation via AMPK/Smad1/5/9 phosphorylation in vitro and in vivo

Chrysophanol (Chrysophanic acid; CA) is a natural anthraquinone found in Senna tora and rhubarb that has various characteristic features, including the ability to suppress adipogenesis. However, its effects on osteoblast differentiation have not been investigated. Herein, this study aimed to demonstrate the mechanism by which CA induces the osteoblast differentiation. CA increased the expression of osteogenic genes. The staining levels Alkaline phosphatase (ALP) and Alizarin Red S (ARS) were increased by chrysophanol. CA induced osteoblast differentiation through AMP-activated protein kinase (AMPK)/Small mothers against decapentaplegic (Smad1/5/9) activation in MC3T3-E1 cells. In addition, compound C, AMPK inhibitor (Comp. C)-induced cells suppressed osteogenic genes expression and AMPK/Smad1/5/9 activation. Interestingly, AMPK in the CA-induced AMPK/Smad1/5/9 signalling pathway was an upstream regulator of Smad1/5/9. In order to further dissect in bone development, we used a zebrafish model to investigate the effect of CA on bone development. These results suggest that CA stimulated bone development via AMPK/Smad1/5/9. Overall, our results demonstrate that CA promotes osteoblast differentiation via AMPK/Smad1/5/9 expression in vitro and in vivo.