Kaempferol promotes bone formation in part via the mTOR signaling pathway

Previous research indicates that kaempferol (Kae) promotes osteogenesis, but its underlying mechanism of action remains unclear. The present study hypothesized that the osteogenic effects of Kae were mediated through mammalian target of rapamycin (mTOR). To validate this hypothesis, bone marrow mesenchymal stem cells (BMSCs) from ovariectomized (OVX) rats were differentiated into osteoblasts. The bone mineral density and bone microarchitecture of the OVX rats was measured in vivo, while osteogenesis was evaluated in vitro via Alizarin Red S staining and alkaline phosphatase activity measurements in cultured BMSCs. The levels of phosphorylated eukaryotic translation initiation factor 4E-binding protein 1 (p-4E/BP1) and phosphorylated ribosomal protein S6 kinase B1 (p-S6K), and the expression of Runt-related transcription factor 2 and Osterix, were concurrently quantified by western blot analysis. The data suggested that Kae prevented OVX-induced osteoporosis in rats by promoting osteoblastogenesis. Furthermore, treatment with Kae in rat BMSCs enhanced mineralization, elevated ALP activity, increased the expression levels of Runx-2 and Osterix and increased the levels of p-S6K and decreased the levels of p-4E/BP1 and, consistent with its ability to promote osteoblast differentiation. In contrast, treatment with rapamycin, an mTOR inhibitor, produced the opposite phenotype. Taken together, these data suggested that the protective effects of Kae in BMSCs and in the OVX rat model resulted from the induction of osteogenesis via mTOR signaling, or at least partially via the regulation of downstream effectors of the mTOR pathway.