Study On The Correlation Between LRP5/6 And Bone Remodeling During Rat Orthodontic Tooth Movement

Objective To investigate the relationship between LRP5/6 and root resorption related indicators,we established rat orthodontic tooth movement model with the same force and local injection of LRP5/6 enhancer(Caprin-2protein),LRP5/6 inhibition(SOST protein)in the mouth,observed the changes in morphology of the periodontal tissues and roots and bone mineral density on the tension side and pressure side of the rat orthodontic tooth at different time points,the expression of LRP5/6,OCN,OSX,RANKL,and osteoclasts in the periodontal tissues was detected to investigate the effect of LRP5/6 on root resorption during orthodontic tooth movement.Methods Thirty-six female SD rats(aged 8-10 weeks)were randomly divided into 3 groups: 35 g group(A group),35 g with Caprin-2 group(B group),35 g with SOST group(C group).Ni Ti tension spring devices were installed in each group and the maxillary bilateral first molars were taken as experimental observation objects.B and C groups were injected with Caprin-2 protein and SOST protein about 50μl on the buccal mucosa near the mesothrum roots of the maxillary bilateral first molars every other day from the day of force application.The concentrations were 4μg/ml and 3μg/ml,respectively.The rats weresacrificed after 3,5,7 and 14 days of orthodontic force application to simulate the occurring of root resorption at different time points.Preparation of maxillary first molars and periodontal tissue paraffin section.The morphological alterations of periodontium on the tension side and pressure side of the orthodontic tooth were observed by HE staining.The expression levels of LRP5/6,OCN,OSX and RANKL in periodontal ligament were determined by immunohistochemical analysis and were measured by Image-pro-plus6.0 image analysis system.The quantity of osteoclasts was examined by TRAP staining.Micro CT measured changes in bone density,trabecular bone,and other bone-related parameters in experimental teeth on the tension and pressure sides.Finally,all the data were analyzed by SPSS16.0 statistical software.Results(1)The orthodontic tooth movement model induced by mechanical force was successfully established in rats.(2)Micro CT results showed that after injection of Caprin-2 protein in group B,Tb.N and Tb.Th were significantly higher than those in group C(P<0.05).After injection of SOST protein in group C,BS/BV and Tb.Sp were significantly higher than those of group A and B,and peaked at the third day(P<0.05).(3)The results of HE showed that bone alveolar resorption and root resorption were similar in group A and B.Absorption of alveolar bone was evident and less root resorption was observed.In group C,not only alveolar bone resorption but also significant root resorption occurred.(4)The results of immunohistochemistry showed that the expression of LRP5/6and OSX in all groups peaked on the third day and then decreased slowly(P<0.05).Under the stimulation of Caprin-2,the expression of LRP5/6 in group B was higher than that of simple plus group and SOST proteingroup(P<0.05),and the expression of OSX was higher than that of SOST protein group(P<0.05).Under the inhibition of SOST,the expression of LRP5/6 and OSX in group C was the lowest among three groups(P<0.05).In group B,under the stimulation of Caprin-2,OCN expression slowly increased from the third day and peaked on the seventh day.The expression level was the highest among the three groups(P<0.05).In group C,under the inhibition of SOST,there was no significant change in the expression of OCN,which was the lowest among the three groups,and the difference was statistically significant(P<0.05).(5)The RANKL immunohistochemistry results of three groups were similar,both slowly increasing from the third day and then peaked on the seventh day(P<0.05).Under the inhibition of SOST,the expression of RANKL in group C was highest in the three groups(P<0.05).The results of TRAP staining showed that the number of osteoclasts in the three groups gradually increased from the third day,and group A peaked at the fifth day,group B peaked at the seventh day,and group C peaked at the fourteenth day(P<0.05).Group C was inhibited by SOST,and the number of osteoclasts was the highest among the three groups(P<0.05).(6)Correlation results showed that LRP5/6 was negatively correlated with BS/BV and RANKL(r<0,P<0.05),and positively correlated with Tb.N,OSX,and OCN(r>0,P<0.05).The BS/BV was positive correlation with RANKL(r>0,P<0.05)and negative correlation with Tb.N,OCN and OSX(r<0,P<0.05).Tb.N is positively correlated with OCN and OSX(r>0,P<0.05)and negatively correlated with RANKL(r<0,P<0.05).There was a negative correlation between OCN and OSX and RANKL(r<0,P<0.05).Conclusion LRP5/6 participates in bone remodeling during orthodontic tooth movement in rats.When LRP5/6 function was inactivated,its ability to regulateosteoblasts decreased,the number of osteoclasts increased,and the expression of RANKL was upregulated.The possibility of osteoporosis increases,and the reconstruction of the alveolar bone mainly as bone resorption.When LRP5/6 was stimulated by Caprin-2,the periodontal tissue remodeling balance had been well maintained.The expression levels of OSX and OCN were similar to or higher than those of the control group,and the effect of promoting bone formation was obvious.