Condylar Bone Remodeling Mechanism Mediated By PLC-γ1_tyr783 After Functional Mandibular Protraction

Objective: The condyle bone remodeling has a direct effect on themorphology and function of the mandibular, it plays an important role onfacial growth and development. The study found that rat chondrocyte areacan be expanded and migrated under periodic mechanical stress, there willalso be a corresponding tissue remodeling on condylar chondrocytes afterexternal mechanical stress stimulation. To the complete the condylar boneremodeling, the body passes external mechanical stress to the body’sendogenous regulatory factors,that is to say change external mechanicalforces signal into biochemical signals.phospholiaseC-gamma1is one of thebody’s endogenous regulatory factors, it plays an important role in celldivision, proliferation and differentiation.PLC-γ1-Tyr783is one of thetyrosine phosphorylation sites, it can be activated by protein tyrosine kinaseor some other endogenous regulatory factors. Ultimately, activated PLCγ1further activates the downstream signaling molecules to promote tissue cellproliferation and differentiation.PLC-γ1_tyr783mediates rat chondrocyteproliferation and matrix synthesis through integrinβ1-Src-Rac1/PLCγ1-ERK1/2under periodic mechanical stress.The purpose of this study was to investigate condylar bone remodelingmechanism mediated by PLC-γ1_tyr783after functional mandibular protractionthrough analyzing the expression and variation of PLC-γ1_tyr783in condylarcartilage during mandibular protrusion, which could provide experimentalevidence for clinical bone orthopedic work.Methods: Sixty4-week-old male Sprague-Dawley rats were used inthis study, weighed about90g. The animals were divided equally andrandomly into6experimental groups （n=5rats） and6control groups （n=5rats）. Functional appliances that were fitted to the upper incisors of animals in the experimental groups were worn24hours a day after being fed for7days by pellets feed, which were self-made. A power chain that was placedacross the head in order to reinforce the retention of the appliances. Theanimals were fed a soft diet both in the experimental and control groups.Inorder to ensure the animal’s weight be the same, we fed the rats in theexperimental group freely and fed the control group regularly. All the ratswere fed water freely. The animals in the experimental groups, together withtheir matched controls, were killed respectively after1,3,7,14,21, and28days. The bilateral condylar were placed in4%paraformaldehyde whichfixed for24hours at4℃, decalcified in10%of the EDTA,dehydrated, andthen conventional Paraffin-embedded. The sections were cut into5μm inthickness. HE staining for histological features, immunohistochemistry ofPLC-γ1_tyr783was applied to observe it’s express distribution and variation.Negative control group with PBS.Results: Experimental rats jaw is moderately protrusive，mandibularposition move forward and downward after removal of the appliance, can’tretreat. The front teeth reach on the edge state.1Histological morphological characteristicThe thickness of the condylar cartilage gradually thinner from back tofront，it was divided into five layers from the cartilage surface to internal.The morphological characteristics of cells in each layer is different. There iscontinuation Between layers. The cartilage below is trabecular and incontinuation with calcified cartilage layer2Immunohistochemical resultsThe expression of PLC-γ1_tyr783was brown which located in cytoplasm.The color of positive cells was significantly higher than background color.The negative control group，PBS instead of first antibody， had no positivestaining granules.2.1Distribution of PLC-γ1_tyr783in the condylar cartilage cell layer.PLC-γ1_tyr783is mainly distributed in the proliferation layer and thebuffer layer, cartilage cell cytoplasm expressed as brownish yellow. 2.2PLC-γ1_tyr783’s expression of posterior condylar cartilage in the controlgroupIn the control group, the expression of PLC-γ1_tyr783decreased gradually,which showed age-related changes. The expression level had no significantdifference on the first, third and seventh day （P>0.05）.On the fourteenthday,compared with the seventh day’s began to appear statisticallysignificant difference（P <0.05）.On the twenty-first day, compared with thefourteenth day’s, the expression level still have significant difference（P<0.05）.On the twenty-eighth day PLC-γ1_tyr783began to maintain a certainlevel, there was no significant difference compared with the twenty-firstday’s （P>0.05）.2.3PLC-γ1_tyr783’s expression of posterior condylar cartilage in theexperimental groupsOn the first day, the expression of PLC-γ1_tyr783in the experimentalgroup is lower than it in the control group, but there was no significantdifference（P＞0.05）.On the third day, the expression of PLC-γ1_tyr783in thecontrol group is lower than it in the experimental group, but there was stillno significant difference（P＞0.05）.On the fourteenth day, the expression ofPLC-γ1_tyr783in the experimental group is much more higher than it in thecontrol group, the expression of PLC-γ1_tyr783began to appear statisticallysignificant difference between the two groups（P <0.05）.On the twenty-firstday, compared with the fourteenth day’s,the expression level have nosignificant difference（P>0.05）.On the twenty-eighth day PLC-γ1_tyr783began to decline, but there was still significant difference compared with thecontrol group（P <0.05）.Conclusions:1The PLC-γ1_tyr783involved in the proliferation and differentiation ofchondrocytes in the growth and development of rat condylar cartilage tissueremodeling process.2The PLC-γ1_tyr783involved in the bone remodeling process of the rat’scondylar cartilage after functional mandibular protraction. 3The mechanical force-biochemical signal transduction of the boneremodeling process of the rat’s condylar cartilage is mediated byPLC-γ1_tyr783.