The Effect Of Osteoblast Targeted Knockout Of STAT3 On Type Ⅶ Collagenase-Induced Osteoarthritis In Mice

Objectives To observe the effect osteoblast-specific knockout of STAT3 in the development of OA in terms of the changes in cartilage and subchondral bone through establishment of an OA model by injecting type VII collagenase into knee joint.Methods Mating OCN-Cre⁺,STAT3^fl/+mice with OCN-Cre^-,STAT3^fl/+to obtain OCN-Cre⁺,STAT3^fl/fl（knockout mice,KO）genotypes and OCN-Cre^-,STAT3^fl/fl（wild-type mice,WT）genotype mice,and the genotypes of the offspring mice were determined by PCR.Take10 weeks old KO and 5 WT male mice produced in the same batch.The left and right legs of the mice were divided into control groups:WT+Vehicle group:WT mice were injected with saline to the knee joint of the left leg;KO+Vehicle group:KO mice were injected with saline to the knee joint of the left leg;WT+Collagenase group:WT small The right knee joint of the mouse was injected with type VII collagenase;the KO+Collagenase group:the right knee joint of the KO mice was injected with type VII collagenase.Mice in the WT+Collagenase group and KO+Collagenase group were injected with 1U/6ul collagenase type VII on the right knee joint at the 0 and 2 days of the experiment.The left knee joint of the WT+Vehicle and KO+Vehicle groups were injected at the 0 and 2 days at the beginning of the experiment.Inject 6ul of normal saline.All mice were sacrificed 42 days later,and samples were taken.Perform immunohistochemistry on all mouse knee joints to observe the expression of STAT3 by osteoblasts（redetermine the genotype）,perform Micro-CT to determine the bone mass and microstructure changes of the subchondral bone,and toluidine blue stain to observe the cartilage tissue morphology learn and perform OARSI histological scoring.All experimental data are statistically analyzed by SPSS20.0 statistical analysis software.Results Micro-CT test results showed that compared with the WT+Vehicle group,the bone mineral density（BMD）of the WT+Collagenase group was significantly reduced,which was statistically significant（P<0.05）,and the trabecular bone volume fraction（percent trabecular area,BV/TV）and trabecular bone number（Tb.N）have a downward trend,but they are not statistically significant.Structural model index（SMI）has no significant difference;compared to KO+Vehicle group,KO+Collagenase group BMD,BV/TV,Tb.N and SMI showed no significant difference;compared with WT+Vehicle group,KO+Vehicle group BMD,BV/TVhas a significant downward trend,There was statistical significance（P<0.05）.Tb.N has a downward trend,but it is not statistically significant.SMI had an upward trend but there was no statistical significance.Compared with the WT+Collagenase group,the KO+Collagenase group had no significant differences in BMD,BV/TV,Tb.N and SMI.STAT3 immunohistochemical results:STAT3 was expressed normally in osteoblasts in WT mice,and STAT3 was not expressed in KO mice.The histological results of toluidine blue showed that:1)Observation of the results of toluidine blue staining showed that:compared with the WT+Vehicle group,the cartilage surface of the WT+Collagenase group was damaged significantly,the number of cartilage cells and the thickness of cartilage and subchondral bone were significantly reduced.The outer matrix was stained unevenly,and staining was lost.Compared with the KO+Vehicle group,there was a small amount of damage to the cartilage surface in the KO+Collagenase group,and the thickness of cartilage and subchondral bone was significantly reduced,but the extracellular matrix staining of cartilage did not appear to be lost.Compared with the WT+Collagenase group,the number of cartilage cells and the extracellular matrix staining of the KO+Collagenase group did not decrease significantly,but the cartilage surface damage was significantly reduced.2)Tibial cartilage OARSI histological score:compared with the WT+Vehicle group,the score of the WT+Collagenase group was significantly higher（P<0.05）;compared with the KO+Vehicle group,the score of the KO+Collagenase group was significantly higher High,statistically significant（P<0.05）;compared to the WT+Collagenase group,the score of the KO+Collagenase group was significantly lower,statistically significant（P<0.05）.Conclusion 1 Targeted knockout of STAT3 gene by osteoblasts can postpone type VII collagenase from inducing mouse OA model.2 Osteoblasts target to knock out STAT3,which protects mouse OA knee cartilage and subchondral bone.Figure 6;Table 8;Reference 155.