The Effect Of TWEAK-p38 MAPK Signaling Pathway On The Pathogenesis Of Periprosthetic Osteolysis

BackgroundPeriprosthetic osteolysis is the predominant reason causing of loosening of artificial hip joints. Wear particles induce monocytes-macrophages, fibroblasts and synovial cells in the tissue surrounding the joints to release inflammatory cytokines, including tumor necrosis factor-a(TNF-a), interleukin-6(IL-6) and monocyte chemoattractant protein-1 (MCP-1). These inflammatory cytokines activate osteoclasts by osteoprotegerin/receptor activator of nuclear factor (NF)-κB ligand and the NF-κB signaling pathway, resulting in loss of bone surrounding the prosthesisTNF-like weak inducer of apoptosis (TWEAK) is a novel member of the TNF superfamily of ligands. TWEAK is involved in a variety of biological processes by binding to its receptor, releasing pro-inflammatory cytokines, regulating the immune response and stimulating apoptosis, and is involved in tissue repair and regeneration. The pro-inflammatory effect of TWEAK has been observed in various cell types, including synovial cells, macrophages, monocytes and osteoclasts. p38 mitogen activated protein kinase (p38 MAPK) is one member of the MAPK family and is involved in regulating cellular responses to external stimuli by intracellular signal transmission (10). The activation of the p38 MAPK pathway activates NF-κB, which is involved in inflammation, by regulating the secretion of pro-inflammatory factors.However, few investigations have been performed on the effects of the p38 MAPK signaling pathway in particle-induced osteolysis, the specific function and mechanism of TWEAK in the pathogenesis of prosthetic aseptic loosening or its correlation with p38 MAPK. Previous studies have demonstrated that TWEAK exhibits pathogenic importance by activating the p38 MAPK signaling pathway in lupus nephritis and myositis diseases.Thus, we did the research as follows to explore the pathogenesis of peripr osthetic osteolysis.1 Expressions and clinical significance of TWEAK and p38 MAPK in patients with aseptic loosening of prosthesesMehtods:The synovium was obtained from patients who underwent surgical procedures for plica syndrome or discoid meniscus, whereas osteoarthritic synovium was obtained from patients who underwent joint replacement for osteoarthritis. Periprosthetic interface membranes were obtained from patients undergoing surgical procedures for aseptic loosening. Tissue sections were stained for general morphological characterization. TWEAK mRNA and p38MAPK mRNA expression in tissues were examined by RT-PCR. Their protein expression were examined by Western blot.ResultsThe osteoarthritic synovial tissue contained more fibrocytes and synovial cells compared with the normal synovial tissue and little inflammatory cell infiltration. Marked inflammatory cell infiltration and hyperplasia of synovial cells were observed in the interface membrane.These findings were further supported by the results of the immunohistochemical analyses. Increased levels of inflammatory cells with positive staining of TWEAK and p-p38 MAPK were observed in the interface membrane, whereas fewer inflammatory cells were observed in the osteoarthritic synovial tissue.The mRNA expression of TWEAK in the interface membrane was markedly higher in the normal tissue compared with the osteoarthritic synovial tissue, whereas the mRNA expression of TWEAK in the osteoarthritic synovial tissue was markedly increased compared with the normal synovial tissue. No significant difference in the mRNA expression of p38 MAPK was observed between the three groups. The expression levels of TWEAK and p-p38 MAPK were increased in the interface membrane compared with the osteoarthritic synovial tissue, whereas the mRNA expression levels of TWEAK and p38 MAPK in the osteoarthritic synovial tissue were higher compared with the normal synovial tissue. No significant difference in the protein expression of p38 MAPK was observed between the three groups.ConclusionTWEAK and p38MAPK are related to aseptic loosening of prostheses and might be involved in the pathogenesis of inflammatory osteolysis.2. The effects of inhibition of p38 MAPK on titanium particles stimulated IL-6 and MCP-1 secretion in macrophageMethods:Cultured macrophage were randomly divided as follows:group A:Control group, group B:A+SB203580, group C:A+TiPs, Group D:A+TiPs+SB203580. TWEAK expression and Phosphorylation of p38mapk expression in cells were examined by Westem blot. The levels of IL-6 MCP-1 in supernatant of cells were measured by ELlSA.Results:Protein expression levels of TWEAK, p38 MAPK and p-p38 MAPK in untreated RAW246.7 cells (Group A) and those treated with p38 MAPK inhibitor (Group B); Ti particles (Group C); or Ti particles+p38 MAPK inhibitor (Group D): the protein expression of TWEAK in group C was higher compared with the other groups (P<0.05) and that the protein expression of TWEAK in group D was higher compared with groups A and B (p<0.05). No significant difference between groups A and B were observed (P>0.05). The protein expression of p-p38 MAPK in group C was higher compared with the other groups (P<0.05) and the protein expression of p-p38 MAPK in group A was higher compared with groups B and D (P<0.05). No significant difference in the protein expression of p-p38 MAPK was observed between groups B and D (P>0.05), and no significant difference was observed in the protein expression levels of p38 MAPK in any of the groups (P>0.05). ELISA results show that:The levels of IL-6 and MCP-1 in group C were higher compared with the other groups (P<0.05). No significant difference was observed between groups A and B (P>0.05).Conclusion:The results demonstrated that the expression levels of TWEAK and p-p38 MAPK increased in the periprosthetic interface membrane tissues and the RAW cells stimulated with Ti particles, suggesting that TWEAK was involved in particle-induced inflammatory osteolysis via the p38 MAPK signaling pathway.3. The effects of inhibition of p38 MAPK on titanium particles-induced murine osteo lysisMethods:In our study, we used C57BL/J6 mice, to observe the degree of bone resorption in a murine osteolysis model. All experimental animals were randomly divided into four groups:control group (Group A), and those treated with p38 MAPK inhibitor (Group B), Ti group (Group C), or Ti particles+ p38 MAPK inhibitor(Group D).Once Ti particles were implanted in mice, the mice were administrated SB203580. After 14 days, the calvaria were collected for histological staining and protein detection.Resultstartrate-resistant acid-phosphatase (TRAP) staing indicated that SB203580 significantly inhibited the generation of TRAP positive cells in a murine osteolysis model, when compared with Ti stimulated calvaria.Levels of TWEAK、IL-6、MCP-1and p-p38 MAPK in the supernatants of cultured in group C were higher compared with the other groups (P<0.05). No significant difference was observed between groups A、B and D (P>0.05).ConclusionThis study showed that SB203580 can remarkable inhibit Ti particle stimulated inflammatory osteolysis by restraining osteoclastogenesis via regulating TWEAK-p38MAPK-IL-6/MCP-1.