The Role Of Lysyl Oxidase-like 2 In Compressive Mechanical Stress-Mediated Matrix Degradation In Rat Mandibular Condylar Cartilage

[Objective]To examine the role of lysyl oxidase-like 2 in compressive mechanical stress-mediated matrix degradation in rat mandibular condylar cartilage, as well as its effect on the inflammation of cartilage.[Method]Ninety-six 7-wk-old male Sprague-Dawley rats were used in this study. On the first day of the experiment, all of the rats in the mechanical force groups were loaded with compressive mechanical force using the appliance which was designed by our group. Rats in each mechanical force group wore the loading appliance for 4 or 7d. Human recombinant LOXL2 (0.44μg rhLOXL2) and anti-LOXL2 antibody (2μg anti-LOXL2) were used to increase or reduce the expression of LOXL2 in chondrocytes in vivo. Histological changes in condylar cartilage were assessed by Hematoxylin & Eosin (HE). Alcian blue staining was used to obverse the change of extracellular proteoglycan. Immunohistochemistry and real-time PCR were performed to evaluate the expression of LOXL2, type Ⅱ collagen and inflammation related factors.[Results]1. Immunohistochemical results revealed that the expression of LOXL2 was slightly decreased at 4 days post mechanical force application, however, the decrease was significant at 7 days post-force application. In addition, the mRNA level of LOXL2 decreased by 18% at 4 days post-force application compared with control group, while it was decreased by 47% at 7 days post-force application.2. With the injection of rhLOXL2 into the temporomandibular joint, the expression of LOXL2 protein level in chondrocytes was increased compared with the MF group. Furthermore, the mRNA level was increased by 13% at 4 days and 34% at 7 days post-force application. In contrast, the expression of LOXL2 was decreased with the injection of anti-LOXL2.3. Increasing the expression of LOXL2 partially rescued mechanical force-mediated mandibular cartilage thinning. The cartilage thickness was increased by 15% at 4 days and 68% at 7 days post-force application, and was reduced by decreasing the expression of LOXL2 at 7 days post-force application.4. Increasing the expression of LOXL2 restored compressive mechanical stress-mediated extracellular proteoglycan degradation by 15% at 4 days and 108% at 7 days post-force application. Also, increasing the expression of LOXL2 restored compressive mechanical stress-mediated collagen Ⅱ degradation by 27% at 4 days and 109% at 7 days post-force application. On the other hand, reducing the expression of LOXL2 promoted compressive mechanical stress-mediated extracellular matrix degradation.5. The inflammation reaction in condylar cartilage was also compromised both at 4 and 7 days post-force application. In contrast, reducing the expression of LOXL2 worsen mechanical force-mediated mandibular cartilage thinning and the degradation of extracellular matrix.[Conclusion]These results demonstrated that LOXL2 played a significantly role in compressive mechanical stress-mediated pathological changes in rat mandibular condylar cartilage especially at 7 days post-force application. Also, rhLOXL2 could protect extracellular matrix from degrading, rescued cartilage thinning and relieve inflammation reaction of cartilage under mechanical force. The inflammation reaction may play a key role in matrix degradation.