Mechanism Of Remodeling In Condylar Cartilage And Bilaminar Zone After Anterior Disc Displacement In Temporomandibular Joint

Epidemiologic studies have shown that temporomandibular joint disorders (TMD) are prevalent in clinic, of which anterior disc displacement (ADD) is the most common type. Studies by arthrography or magnetic resonance indicated not all persons with disc displacement would develop to TMD. More than 1/3 persons free from signs and symptoms had evidence of ADD. Without recovering the nomal location of the disc, conservative treatment to the patients with symptoms would also be effective.TMJ is a burdened joint which keeps strong ability of remodeling in all life. The loading on TMJ is of important significance in maintaining the structure and function of every component. After ADD, the mechanical environment changes in TMJ could make a series of adaptive changes to adapt to the changed disc-condyle position. As the primary loading areas, condyle and disc were paid a good many attentions by researchers. Previous studies showed, in the early stage of ADD,the condyle cartilage extracellular matrix degraded, however, with the ADD developed, it could recover and in the anteriorly displaced bilaminar zone (BZ), more and more chondrocytes appeared and cartilage areas formed, which made the BZ become disc-like tissue to function as a disc. To explore the mechanism of TMJ remodeling and provide some theory evidence and guidance to the clinic treatment scheme of ADD, this subject was divided into two parts: c-fos gene transcription and expression, TGF-β1, BMP-2 and OPG/OPGL expression in condylar cartilage were examined by immunohistochemistry and in situ hybridization methods, and TGF-β1 BMP-2 mRNA and the activation of P-38 and JNK in BZ were detected by RT-PCR and western-blot methods..Section OneMechanism of adaptive changes in condylar cartilage after anteriordisc displacementMETHODS: Thirty-three healthy adult Japanese rabbits (from medical animal center of Zhejiang University) weighing from 2 to 3 kg were used in this study. Twenty-five rabbits were subjected to surgical anterior disc displacement in the right temporomandibular joints and every 5 rabbits were sacrificed 1, 2, 4, 8, 12 weeks post-operation;5 rabbits were used as sham-operative control and every one rabbit was sacrificed 1, 2, 4, 8, 12 weeks post-operation.The other three without operation were used as normal control. The gene transcription and expression of c-fos in condylar cartilage were studied by in situ hybridization and immunohistochemical methods. The expression of TGF-pl , BMP-2 , OPG and OPGL in condylar cartilage were also detected by immunohistochemical method. The stainings by in situ hybridization and immunohistochemical methods were measured with FJY Image Computer Analysis Software. Data were statistically analyzed by one-way ANOVA and t test.RESULTS: The results showed, experimental and sham-operative animals tolerated the surgical procedures well;the discs were anteriorly displaced successfully in all experimental rabbits. Little c-fos mRNA or protein were detected in control group, 1-2 weeks after ADD, gene transcription and expression of c-fos increased significantly (P <0.05) . Four weeks after ADD, the gene transcription and expression of c-fos began to decrease;8-12 weeks after ADD, the gene transcription and expression of c-fos almost came back to the level before ADD.fn control group, TGF-pi staining was moderate and mostly expressed in the hypertrophic layer and calcified cartilaginous layer, while BMP-2 staining was weak and mostly expressed in the proliferative layer and transitional layer. After ADD, the staining for TGF-pi and BMP-2 became stronger, and the positive cells increased. There was significant difference in the average staining gray degree between the control group and experimental group (P<0.05) . In 8 weeks group after ADD, the cells in all layers of mandibular condylar cartilage almost expressed TGF-pi and BMP-2.OPG and OPGL only weakly expressed in the condylar cartilage of control group. However, after ADD the expression of OPG and OPGL were stronger. There was significant difference in average gray degree of OPG and OPGL (P<0.05) between the experimental and control groups, but the ratio of OPG/OPGL was stable (P>0.05) .Section TwoMechanism of adaptive changes in bilaminar zone after anterior discdisplacementMETHODS: Twenty-eight healthy adult Japanese rabbits (from medical animal center of Zhejiang University) weighing from 2 to 3 kg were used in this study. Twenty rabbits were subjected to surgical anterior disc displacement in the right temporomandibular joints, every 5 rabbits were sacrificed 1, 2, 4, 8 weeks post-operation, 5 rabbits were used as sham-operative control and the other3 without operation were used as normal control. The mRNA levels ofTGF-p 1 and BMP-2 in bilaminar zone (BZ) were detected by RT-PCR method. The expression of Phosphated- P38, Phosphated-JNK , P38 and JNK in bilaminar zone were examined by western-blot method and the activation of P38 and JNK were evaluated.RESULTS: In the control group, the mRNA levels of TGF-p 1 and BMP-2 were low, 1-2 weeks after ADD, the TGF-pl and BMP-2 mRNA level increased significantly (P <0.05) . 4 weeks after ADD, the BMP-2 mRNA level increased to peak, 8 weeks after ADD, the BMP-2 mRNA level decreased lightly. However, the mRNA levels of TGF-pi increased persistently.The activation of P-38 in 1 week group was enhanced compared with control group, in 2 and 4 week group, the activation continued to be enhanced. In 8 week group, the activation of P-38 decreased but was still stronger than that in control group. However, after ADD, few JNK-1 activation was found, and JNK-2 slightly activated just in early stage.CONCLUSIONS1. The gene transcription and expression of c-fos in mandibular condylar cartilage were significantly increased in the early stage of ADD. It suggested that c-fos might play an important role in the signal transduction in the remodeling of the mandibular condylar cartilage after ADD.2. The location and quantity of TGF-pl and BMP-2 in condylar cartilage changed after ADD, and these changes were consistent with the development of ADD. It suggested that TGF-pi and BMP-2 might regulate the remodeling of the mandibular condyle induced by the mechanical stimulation during the disc displacement.3. OPG and OPGL could express harmoniously in the condylar cartilage, which played an important role in maintaining the metabolism balances of condylar cartilage. OPG and OPGL might involve in the development and prognosis of the temporomandibular condylar cartilage adaptive alterations after ADD.4. TGF-p 1 and BMP-2 mRNA level in bilaminar zone increased after ADD. TGF-p 1 and BMP-2 might induce other phenotype cells in synovial tissue or other tissues of BZ to chondrocyteand involved in the adaptive remodeling of BZ after ADD.5. After ADD, the activation of P38 increased significantly, however few or a few JNK was activated. The results might suggest in the remodeling of BZ after ADD, the P38 pathway play an important role, however, the JNK pathway play minor role. The activation of P-38 might involve in the chondrogenesis in BZ.