The Mechanism Of Protein Phosphatase 2A In Regulating Macrophage M1 Polarization In Inflammatory Osteolysis Induced By Wear Particles

Objective:Chronic inflammation is the occurrence and concomitant process of many diseases.It is usually a continuous state in which white blood cells continuously flood into damaged tissues through the regulatory role of macrophages in the inflammatory environment.Macrophages can be activated and polarized to form different pro-inflammatory phenotype M1 and anti-inflammatory phenotype M2 in the chronic inflammatory environment to participate in the regulation of inflammatory response.Protein phosphatase 2A(PP2A)is a serine threonine phosphatase which can regulates most of the phosphorylating enzymes in eukaryotic cells.PP2A has important effects on tumorigenesis,embryonic development and chronic respiratory diseases.However,the relationship between PP2A and chronic inflammatory responses and the effect of PP2A on macrophage phenotypic polarization are not fully understood.Therefore,our experiment aims to explore the effect of PP2A on chronic inflammatory response and whether it can activate and induce polarization of macrophages to participate in the regulation of inflammatory response.We hope to provide a theoretical basis for PP2A treatment of periprosthetic osteolysis caused by aseptic inflammatory response.Methods:Forty 6-week-old male C57BL/J6 mice were selected to construct a mouse skull osteolysis model induced by sterile titanium particles.Randomly divided the mice into four groups:blank control group,model group,low dose treatment group and high dose treatment group.Titanium particles were implanted on the surface of the skull.0.4 g/kg and 4 g/kg of Okadaic Acid(OA)solution dissolved in PBS were injected daily under the scalp of the low-dose and high-dose treatment groups.The model group and the blank control group were given the same amount of sterile PBS.Killed the mice two weeks later and collect their skulls.Micro-CT scanning and histological staining were performed to obtain the results.BMMs were used to investigate the effect of PP2A inhibition on macrophage phenotypic polarization in vitro.Results:According to the results observed in micro-ct reconstruction,compared with the model group,the bone density(BMD)and bone volume/total volume(BV/TV,%)of the mice in the OA treatment group showed different degree of increase.H&E staining showed a significant decrease in bone surface erosion and periosteal thickness in the treatment group,while TRAP staining showed a significant decrease in the number of osteoclasts in the treatment group.The results of IHC staining confirmed that the number of proinflammatory cytokines TNF-α,il-1β and il-6 increased in the treatment group,while the number of anti-inflammatory cytokines il-10 decreased,and the expression of IKKαand P65 decreased in the NF-kB signaling pathway.Co-localized immunofluorescence staining showed that in the treatment group,the proinflammatory phenotype M1 was decreased while the anti-inflammatory phenotype M2 was increased.In addition,cellular immunofluorescence staining demonstrated that inhibition of PP2A expression in vitro resulted in a decrease in macrophage pro-inflammatory M1 phenotype and an increase in anti-inflammatory M2 phenotype.Conclusions:The results of this experiment demonstrated that inhibiting the expression of PP2A can reduce the degree of bone destruction in inflammatory osteolysis induced by titanium particles and reduce the inflammatory reaction.At the same time,it has also been proved that PP2A can reduce inflammation by inhibiting NF-kB signaling pathway to activate and induce macrophage phenotype polarization.These results suggest that PP2A can be used as a new research direction to alleviate and treat chronic inflammatory reactions and reduce the incidence of failure and revision caused by osteolysis around prosthesis after total joint replacement.