Nobiletin, a NF-κB signaling antagonist, promotes BMP-induced bone formation

The NF-kappa B family of transcription factors plays an important role in skeletal development and bone homeostasis. In osteoblast cells, NF-kappa B signaling has been shown to suppress survival, proliferation, and differentiation. Furthermore, pharmacological suppression of NF-kappa B enhances osteoblast differentiation and bone formation. Thus, NF-kappa B antagonists are promising candidates as anabolic agents for enhancing bone mass. In this study, we describe the mechanism by which nobiletin, an inhibitor of NF-kappa B activity, regulates osteoblast differentiation and mineralization. We found that in MC3T3-E1 osteoblast cells, nobiletin inhibited a TNF-alpha responsive NF-kappa B luciferase reporter and also decreased the induction of classical NF-kappa B target genes by TNF-alpha. Consistent with this, nobiletin prevented TNF-alpha -mediated suppression of osteogenesis and potently enhanced the differentiation and mineralization of MC3T3-E1 cells. Likewise, in an in vivo BMP2-induced ectopic bone formation assay, nobiletin markedly enhanced ossicle bone volume. Western blotting and SMAD-responsive luciferase assays also demonstrated that NF-kappa B suppression of BMP signaling could be inhibited by nobiletin. Thus, our data suggest that mechanistically, nobiletin prevents the endogenous repression of BMP signaling by TNF-alpha, thereby enhancing osteoblast activity. In conclusion, nobiletin is a novel NF-kappa B antagonist that may be a useful anabolic agent for bone formation.