Mechanism of the bone morphogenetic protein 2 inducing osteoclast activation in the mouse model

ObjectiveTo investigate the role of bone morphogenetic protein 2 (BMP-2) in inducing the osteoclast activation in mice, and its related mechanisms.

MethodsTwenty mice were randomly divided into the control group and experimental group (10 mice in each group), and treated with intertransverse fusion surgery through the posterolateral approach of the spine.The experimental group was implanted with bone fragments combined with BMP-2, the control group was only implanted with bone fragments, and the postoperative bone changes in two groups were evaluated.The bone marrow-derived macrophages (BMMs) were extracted from the tibia of the mice, induced into osteoclasts using RANKL and M-CSF reagents, and co-cultured with different concentrations of BMP-2.The osteoclasts, mRNA levels of Smad1 and p65 and protein levels of Smad1 and p65 were detected using TRAP staining, RT-PCR and Western blot, respectively.

ResultsThe results of image examination of micro-CT showed that the spinal fusion in experimental group was stronger than that in control group.The trabecular bone volume and trabecular thickness in two groups showed an increasing trend after 1, 2 and 4 weeks of operation, and the trabecular bone gap showed a decreasing trend, and the difference of which was statistically significant (P < 0.05).The volume of trabecular bone in experimental group was higher than that in control group at 1, 2, and 4 weeks after operation, and the trabecular space in experimental group was lower than that in control group at 2 and 4 weeks after operation (P < 0.01).The total number and total area of osteoclasts at the 60 ng/mL, 90 ng/mL and 120 ng/mL of BMP-2 were higher than those at 0 ng/mL and 30 ng/mL of BMP-2 (P < 0.01).The differences of the expression levels of Smad1 and p65 mRNA in osteoclasts induced by different concentrations of BMP-2 were statistically significant (P < 0.01), and the expression level of Smad1 mRNA was linearly correlated with p65 (P < 0.01).The differences of the expression levels of Smad1 and p65 protein in osteoclasts induced by different concentrations of BMP-2 were statistically significant (P < 0.01), and the expression level of Smad1 protein was linearly correlated with p65 (P < 0.05).

ConclusionsBMP-2 can promote the fusion of mouse spinal surgery model.BMP-2 is involved in the process of osteoclast activation, and may mediate osteoclast activation via Smad1/p65 signaling pathway.