| Background:Malocclusion,which is one of the most frequently encountered diseases in stomatology,has a very high incidence.Nowadays more and more people pay attention to the disease.The insufficient maxillae,one of common malocclusions,can affect language,chewing and other functions,and affects beauty and the physical and mental health.Stenosis or crowding,which was resulted from the insufficient maxilla,can be corrected by rapid maxillary expansion(RME)in the clinical treatment.RME is a typical sutural distraction osteogenesis technique.Through the expansion of opening loops,the fibrous tissue links of the palate suture was opened.The width of the maxilla and dental arch were expanded by active bone remodeling.However,it needs a long time for new bone formafion and mineralization after RME,or it will be quite easy to relapse.In most cases,the new bone formation will be affected by many factors and absorbed again.Thus the maxilla and dental arch become narrow again.The incidence of relapse is very high.So accelerating bone remodeling in the mid-palatal suture is a vital process to shorten the retention period after RME.It has been reported that growth factors,drugs,physical stimuli,et al.could effect the speed of bone remodeling after RME.But no studies have investigated the factors at a post-transcriptional level.miRNA,a type of endogenous non-coding RNA molecule,regulates the expression of genes mainly at the post-transcriptional level.It is widely involved in a series of important processes,including cell differentiation,biological development,diseases,development,etc.Recently,many studies have shown that miR-21 is closely related to the osteogenic differentiation of stem cells.Our previous microarray analysis found that many genes miR-21 targeted were significantly enriched in signaling pathways related to osteogenic differentiation.In addition,previous experiments have confirmed that miR-21 can promote osteoblast differentiation of periodontal ligament stem cells in vitro.However,the effect of miR-21 on bone remodeling in the mid-palatal suture caused by RME is not yet clear.In this study,the effect of miR-21 on the remodeling of the palatel suture after RME was analyzed at a post-transcriptional level.Purpose:This research aimed to study the effects of microRNA-21 on the midpalatal suture remodeling by expand the palatal sutures of both mmu-miR-21-deficient(miR-21-/-mice and Wild-type(WT)mice.Materials and Methods:First,we perchased the miR-21-/-mice and verify the genotype with the application of agarose gel electrophoresis and real-time quantitative PCR.According the genotype ofmice,they were divided into 2 groups:WT(A group),miR-21-/-(B group).Then they were divided into two subgroups according to different adenovirus:non-expansion groups(Study groups:A1 group and B1 group)and expansion groups(Control groups:A2 group and B2 group).There was nothing done in the group A1 and B1.The opening loop expander was inserted into the mice’s molars in the group A2 and B2.After activated,the expander would genetate the force(0.49N).The mice were euthanized on the 1st,3rd,7th,14th,28th days.Paraffin sectionh were used for ematoxylin-eosin staining(HE),tartrate-resistant acid phosphatase(TRAP),immunohistochemistry staining(eg.ALP,OCN,OPG,RANKL).Results:1.The results of agarose gel electrophoresis and real-time quantitative PCR showed that miR-21 was knocked out in miR-21-/-mice.2.Overall observation:On the 2th and 3th day after the expansion,the weight went down in the two expansion groups.And they rose on the 4th day.The everage weights in the two expansion groups were less than that in control groups on the whole period(P<0.05).With the macroscopic observation,the maxillary width in groups A2 and B2 was wider than the group A1 and B1.3.HE results:In the groups A1 and B1,the structure of the maxilla remained almost the same.There were few chondrocytes and osteoblast,which became mature.The fibrous tissue in the midpalatal suture of the groups A2 and B2 were streched wider and cartilaginous components grew into the fibrous tissue.Some osteoblasts proliferated and became activein the suture margine.On the 14th and 28th days,compared with that in the group B2,new bone and cells were much more in the group A2.4.TRAP results:In the groups A1 and B1,there were fewer osteoclast when compared to A2 and B2.At the same time,the number of osteoclast in group B1 was significant lower that group A1.The osteoclast in midpalatal suture of the groups A2 and B2 increased after RME.While the osteoclast in group B2 is more than that in group A2(P<0.05).6.Immunohistological results:Under physiological conditions,there was no significant difference in ALP expression between the A1 group and the B1 group.However in the group of 28 day,the expression level in the B1 group was higher than that in the A1 group(P<0.05).After RME,the expression of ALP gene in mice of group A2 was significantly higher than that of group B2 in the early period.In the later period,the mice in group A2 basically recovered histological morphology,and the expression level of ALP decreased.In group B2,the osteoblast increased and the expression of ALP increased(P<0.05).Besides,the MOD value of OCN in the group A was higher than the MOD value in the group B.MOD value of RANKL/OPG in the group A1 was more than that of the group B1,while MOD value of RANKL/OPG in the group B2 is high than that of A2(P<0.05).Conclusion:1.Without expanding force,miR-21-/-mice and WT mice had no significant difference in osteogenesis,but miR-21-/-could inhibit osteoclasts formation in the maxillary palate.2.After RME,there is a big significance of miR-21-/-mice and WT mice in osteogenesis.miR-21-/-mice were able to delay the formation of osteoblasts in the maxillary palatal suture.Under the force of mechanical,due to the breakage of the osteogenesis and osteoclast balance,more osteoclasts were formed in miR-21-/-mice.Whereas the number of osteoblasts in WT mice was more than that in osteoclasts.3.miR-21 can promote bone remodeling after maxillary rapid expansion. |
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