Bone fracture healing is a complex, dynamic process that involves various cell types, with osteoclasts and osteoblasts playing indispensable roles. In this study, we found that psoralen, the main active ingredient in Psoralea corylifolia L. fruit extract, enhanced bone fracture healing through activation of osteoclast and osteoblast activity via the ERK signaling pathway. In detail, psoralen promoted receptor activator of nuclear factor‐κB ligand‐induced osteoclastogenesis, mRNA expression of osteoclast‐specific genes, and osteoclastic bone resorption in primary bone marrow‐derived macrophages. Meanwhile, psoralen induced osteogenic differentiation by promoting the mRNA expression of the osteoblast differentiation markers alkaline phosphatase, runt‐related transcription factor 2, osterix, and osteocalcin. At the molecular level, psoralen preferentially activated ERK1/2 but not JNK or p38 MAPKs. Further experiments revealed that psoralen‐induced osteoclast and osteoblast differentiation was abrogated by a specific inhibitor of phosphorylated ERK. In addition, psoralen accelerated bone fracture healing in a rat tibial fracture model, and the numbers of osteoclasts and osteoblasts were increased in psoralen‐treated fracture callus. Taken together, our findings indicate that psoralen accelerates bone fracture healing through activation of osteoclasts and osteoblasts via ERK signaling and has potential as a novel drug in the orthopedic clinic for the treatment of bone fractures.—Zhang, T., Han, W., Zhao, K., Yang, W., Lu, X., Jia, Y., Qin, A., Qian, Y. Psoralen accelerates bone fracture healing by activating both osteoclasts and osteoblasts. FASEB J. 33, 5399–5410 (2019). http://www.fasebj.org

Osteoporosis is an osteolytic disorder commonly associated with excessive osteoclast formation. Transcriptional coactivator with PDZ-binding motif (TAZ) is a key downstream effector of the Hippo signaling pathway; it was suggested to be involved in the regulation of bone homeostasis. However, the exact role of TAZ in osteoclasts has not yet been established. In this study, we demonstrated that global knockout and osteoclast-specific knockout of TAZ led to a low-bone mass phenotype due to elevated osteoclast formation, which was further evidenced by in vitro osteoclast formation assays. Moreover, the overexpression of TAZ inhibited RANKL-induced osteoclast formation, whereas silencing of TAZ reduced it. Mechanistically, TAZ bound to TGF-activated kinase 1 (TAK1) and reciprocally inhibited NF-κB signaling, suppressing osteoclast differentiation. Collectively, our findings highlight an essential role of TAZ in the regulation of osteoclastogenesis in osteoporosis and its underlying mechanism.

Osteosarcoma is the most common malignant bone tumor. Most patients diagnosed with osteosarcoma are less than 20 years of age. Osteosarcoma cells proliferate rapidly and invade other tissues. At present, neoadjuvant chemotherapy is the primary pharmacodynamic strategy to prevent the progression of osteosarcoma. However, adverse effects of this strategy limit its long-term application. Previous research has shown that fangchinoline exerts antitumor effects on several types of tumor cells; however, its effect on osteosarcoma cells remains unknown. The present study evaluated the effects of fangchinoline on the proliferation, apoptosis, migration and invasion of osteosarcoma cells in vitro and on their tumorigenesis in vivo and determined the possible underlying mechanism of action. Fangchinoline-treated MG63 and U20S cells showed significantly decreased proliferation and significantly increased apoptosis. Fangchinoline markedly suppressed the migration and invasion of the MG63 cells. Fangchinoline-treated MG63 cells showed significantly decreased expression of phosphoinositide 3-kinase (PI3K) and Aktp-Thr308. Moreover, fangchinoline-treated MG63 cells showed downregulated expression of cyclin D1 and matrix metalloproteinase 2 and 9, which act downstream of PI3K, and upregulated expression of caspase-3 and caspase-8. Furthermore, fangchinoline suppressed the growth of subcutaneous osteosarcoma tumors in Balb/c mice subcutaneously injected with osteosarcoma cells. These findings suggest that fangchinoline inhibits the progression of osteosarcoma by suppressing the proliferation, migration and invasion and by accelerating the apoptosis of osteosarcoma cells. In addition, our results suggest that the mechanism underlying the antitumor effects of fangchinoline involve the inhibition of PI3K and its downstream signaling pathways.

Osteoclasts (OCs) are multinuclear giant cells responsible for bone resorption, and an excessive bone resorption by OCs plays an important role in osteoporosis. Commonly used drugs for the treatment of osteoporosis have severe side effects. As such, identification of alternative treatments is essential. Garcinol, a polyisoprenylated benzophenone extracted from the fruit of Garcinia indica, has shown a strong antitumor effect through the nuclear factor-κB (NF-κB) and mitogen-associated protein kinases (MAPK) signaling pathways. However, the role of garcinol in the osteoclastogenesis is still unclear. Here, we demonstrated that garcinol can inhibit the receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis, osteoclastogenesis-related gene expression, the f-actin ring, and resorption pit formation. In addition, garcinol abrogated RANKL-induced osteoclastogenesis by attenuating the degradation of the MAPK, NF-κB, and PI3K-AKT signaling pathway as well as downstream factors c-jun, c-fos, and NFATC1. In vivo, suppression of osteoclastogenesis by garcinol was evidenced by marked inhibition of lipopolysaccharide-induced bone resorption. In conclusion, our data demonstrated that garcinol inhibited the RANKL-induced osteoclastogenesis by suppressing the MAPK, NF-κB, and PI3K-AKT signaling pathways and thus has potential as a novel therapeutic option for osteolytic bone diseases.

Osteolytic diseases are characterized by an increase in the number and/or activity of bone‐resorbing osteoclasts. Identification of natural compounds that can suppress osteoclast formation and function is crucial for the prevention and treatment of osteolytic diseases. Vitexin, a naturally‐derived flavonoid extracted from various medicinal plant species, demonstrates a broad range of pharmacological properties including anticancer and anti‐inflammatory effects. Here in this study, we showed that vitexin exerts antiosteoclastogenic effects by directly inhibiting receptor activator of nuclear factor‐κB ligand (RANKL)‐induced osteoclast formation and bone resorption in vitro and protected against lipopolysaccharide (LPS)‐induced inflammatory osteolysis in vivo. Vitexin suppressed the early activation of ERK and p38 MAPK pathways in response to RANKL thereby attenuating the downstream induction of c‐Fos and NFATc1, and abrogating the expression of osteoclast marker genes. Collectively, these results provide evidence for the therapeutic application of vitexin in the treatment of osteoclast‐mediated bone lytic diseases.

Osteosarcoma is the most common malignant bone tumor that frequently affects adolescents. Osteosarcoma cells tend to proliferate and invade other tissues such as those of the lungs. Currently, neoadjuvant chemotherapy is the primary strategy to prevent tumor progression. However, its adverse effects result in poor long-term outcomes. Previous research has shown that galangin exhibits antitumor properties on several types of cancer cells; however its effect on osteosarcoma cells is yet unknown. The aims of this study were to evaluate the effects of galangin on the proliferation, apoptosis, migration, and invasion of osteosarcoma cells and to explore the underlying mechanisms. We found that the proliferation of MG63 and U20S osteosarcoma cells decreased significantly, while the apoptosis of MG63 cells accelerated significantly after exposure to galangin. In addition, the migration and invasion of MG63 cells were significantly inhibited by galangin. Moreover, phosphoinositide 3-kinase (PI3K) and Aktp-Thr308 expression levels were found to be significantly lower in galangin-treated MG63 cells than in the control cells, and the protein expression levels of their downstream regulators cyclin D1 and matrix metalloproteinase 2/9 were also downregulated in galangin-treated groups, while those of p27Kip1, caspase-3, and caspase-8 were upregulated. These findings suggest that galangin suppresses osteosarcoma cells by inhibiting their proliferation and invasion and accelerating their apoptosis, and the mechanism may be associated with the inhibition of PI3K and its downstream signaling pathway.

Bone callus, generated during fracture healing, is commonly discarded during surgical procedures. The aim of this study was to investigate the osteogenic potential of bone callus and its possible use as autograft material for patients needing bone grafts. Histology, immunohistochemistry, micro-computed tomography, and biomechanics were performed to examine osteogenic cells, osteoinductive factors, and the osteoconductive structure of bone callus. Alkaline phosphatase-positive osteoblasts, osteoinductive factors (including BMP2, FGF2, TGFB1, and IGF1), and a porous structure were found in bone callus. Early-stage callus (within 3 months after fracture) presented significantly improved osteogenic properties compared to medium- (3–9 months) and late-stage (longer than 9 months) callus. The results revealed that bone callus induced new bone formation in a nude mouse model. Early-stage callus showed better performance to medium- and late-stage callus in the induction of new bone formation at both 8 and 12 weeks. These findings indicated that bone callus, especially early-stage callus, possesses osteogenic potential and can potentially serve as an alternative source of material for bone grafts.

Osteoclasts (OC) are critical cells responsible for many bone diseases such as osteoporosis. It is of great interest to identify agents that can regulate the activity of OC to treat osteolytic bone diseases. In this study, we found that baicalin exerted a two‐way regulatory effect on OC in a concentration‐dependent manner in vitro and in vivo. In detail, baicalin at a low concentration (below 1 μmol/L) enhanced OC differentiation and bone resorption, but baicalin at a high concentration (above 2 μmol/L) exhibited inhibitory effects on OC. We demonstrated that baicalin at low concentrations enhanced the mitogen‐activated protein kinase (MAPK) (ERK) signalling pathway and activated c‐Fos and NFATc1 expression, and thus enhanced gene expression, OC differentiation and bone resorption. However, baicalin at higher levels not only suppressed ERK phosphorylation and c‐fos and NFATc1 expression, but also altered the expression of apoptosis‐related proteins, and therefore inhibiting OC function. This dual effect was further verified in an LPS‐induced mouse calvarial osteolysis model, evidenced by enhanced osteolysis at a lower concentration but reduced bone loss at a higher concentration. Overall, our findings indicate that baicalin exerts dose‐dependent effects on OC formation and function. Therefore, caution should be applied when using baicalin to treating OC‐related bone diseases.