The Role And Mechanism Of BRD4 Protein In Periprosthesis Osteolysis Induced By Wear Particles

Objective: To probe into the function and machine-processed of bromodomain-containing protein 4(BRD4)on PPOL mediated by wear debris.By studying the role and mechanism of local BRD4 in the bone tissue in the titanium(Ti)particle-induced mouse skull osteolysis model,we can further reveal the pathological mechanism of the pathogenesis of wear particle-induced PPOL,and lay a theoretical basis for its diagnosis and treatment.Methods: In the first part of the experiment,BRD4 protein expression was detected in the boundary membrane tissue of PPOL patients or the synovial tissue of people undergoing total hip arthroplasty for the first time due to fracture.The cell morphology and BRD4 protein distribution of the above two tissues were observed by hematoxylin-eosin staining and immunohistochemistry.In this study,Western Blot and RT-QPCR were used to analyze and compare the expression of BRD4 in the above two tissues.In the second part of the experiment,a total of 30 8-week-old C57BL/6J mice were splited into three groups:Sham group,Ti group and Ti+JQ1(BRD4 inhibitor)group(10 mice/group).Ti particles were surgically added to the top of the skull of mice to induce osteolysis.JQ1(50 mg/kg)was injected into the abdominal cavity of mice in Ti+JQ1 group on the 2nd day after surgery,and the same amount of solvent was injected into the abdominal cavity of mice in Sham group and Ti group every 2 days for 2 weeks.Executed in mice after skull organization measure the content of the BRD4,micro CT is also used to mice on the surface of the skull bone content and porosity were analyzed,and through the hematoxylin and eosin staining on bone dissolve degree,through the tartrate resistant acid phosphatase(TRAP)staining in the skull on the groups of mice osteoclast statistical comparison,Finally,m RNA and protein of RANKL/ RANK signaling pathway were detected and analyzed.T test or one-way ANOVA were used to analyze the experimental data.Results: Hematoxylin-Eosin staining showed that the inflammatory level of human boundary membrane tissue was higher than that of synovial tissue.Immunohistochemistry,Western-blot and RT-QPCR showed that BRD4 was expressed in the above two tissues,but the level of BRD4 in the boundary membrane tissue was significantly taller than that in synovial tissue(p<0.05);In the second part of the experiment,the level of BRD4 in Ti group was taller than that in the other 2 groups(p<0.05).Micro-CT analysis showed that the bone damage degree of Ti group was more serious than that of Sham group,while the bone damage degree of Ti+JQ1 group was prominently lower than that of Ti group(p<0.05);Further analysis showed that BMD and BV/TV in Ti group were prominently less than those in Sham group and Ti+JQ1 group,while the comparison of surface porosity was opposite(p<0.05).The results of hematoxylin-eosin staining showed that the osteolysis degree of skull tissue in Ti group was higher than that in Ti+JQ1 group and Sham group.The results of tartrate-resistant acid phosphatase staining showed that the surface area of osteoclasts(OC.S/BS),Ti group’s number of osteoclasts and ES/BS were higher than those in Sham group and Ti+JQ1 group(p<0.05).Western blot and RT-QPCR showed that Ti group’s levels of RANKL/ RANK signaling pathway were highest in all groups(p<0.05).Conclusions: BRD4 is expressed in the boundary membrane tissue of patients with periprosthetic osteolysis and synovial tissue of patients undergoing total hip arthroplasty for the first time due to fracture,but the level is higher in the boundary membrane tissue.It was found that BRD4 has an effect on RANKL/ RANK signaling pathway and induces osteoclasts to participate in the pathogenesis of osteolysis induced by wear particles,and the inhibitor JQ1 of BRD4 protein has a protective effect on local osteolysis induced by Ti particles in skull of mice.