ABSTRACT
Objectives To observe the effect of low intensity pulsed ultrasound (LIPUS) on osteocyte injuries induced by the tricalcium phosphate(TCP) wear particles in the calvaria of mice.Methods Thirty ICR male mice of 6 to 8 weeks were randomly divided into a normal control group(n=10),a model group (n=10) and a LIPUS-treated group(n=10).A murine calvarial model of osteolysis was established in the model and LIPUS-treated groups through injecting TCP particles onto the surface of bilateral parietal bones at week 1,3,5,7 and 11.Mice in the normal group received negative ultrasound probe pressing,while those in the LIPUS-treated received LIPUS radiation.Three months later,the calvarias were obtained.The micro-CT,HE staining,flow cytometry and Western blotting were performed to estimate the calvarial osteolysis,osteocyte death,apoptosis and proteins expression of the dentin matrix protein 1 (DMP-1),sclerosis protein (SOST),glucose-regulated protein78 (GRP78),inositol-requiring enzyme(IRE 1 α),spliced X-box binding protein 1 (XBP1 s),c-Jun N-terminal kinase (JNK) and phosphorylated c-Jun N-terminal kinase(p-JNK) respectively.Results Compared with the normal control group,in the model group the viability of prosthetic osteocytes decreased significantly,and cell apoptosis was more obvious(P＜0.05);the osteocytic marker protein DMP-1 down-regulated significantly,but another marker protein SOST up-regulated significantly,which caused the decline in DMP-1/SOST(P＜0.05).Moreover,the expression levels of GRP78,IRE1,XBPls and p-JNK of the model group increased significantly(P＜0.05) in the calvaria osteocytes compared to the control group.However,in the LIPUS treatment group,osteocyte injuries and endoplasmic reticulum(ER) stress both decreased significantly,shown by a significant increase in the number and activity of osteocytes,DMP-1/SOST,and significant inhibition of the IRE1α-XBP1-JNK activation(P＜0.05).Conclusion LIPUS prevents osteocyte injuries induced by TCP wear particles in the calvaria of mice,which may be due to the inhibition of IRE1α-XBP1-JNK pathway activation through ER stress reaction.