[Effect of different mechanical loading on the expression of Notch signaling pathways in growing rabbits' condylar cartilage]

Objective: To investigate the effect of different mechanical loading on the expression of Notch-1, Notch-3, Jagged-1 and Delta-like-1 in growing rabbits' condylar cartilage. Methods: Sixty-four ten-days-old rabbits were randomly divided into experimental and control groups. The rabbits in the experimental groups were fed on a powder diet, while the control groups were fed on a solid diet. The animals were sacrificed after 2, 4, 6 and 8 weeks. Notch-1, Notch-3, Jagged-1 and Delta-like-1 gene and protein expressions were examined by HE, immunohistochemistry, Western blotting and quantitative real-time PCR. Results: At 2, 4, 6, 8 weeks, the anterior part of condylar cartilage in solid diet groups ([318.1±4.3], [342.4±2.6], [364.2±3.2], [380.7±6.0] mm, respectively) were thicker than those in powder diet groups ([275.4±2.6], [301.1±2.0], [322.3±3.3], [366.5±8.4] mm, respectively) (P<0.05). There was no significant difference between the two groups in the middle part (P>0.05). From 2 to 6 weeks, the posterior part of cartilage in solid diet groups ([444.1±1.5], [451.1±0.3], [476.4±5.7] mm, respectively) was thinner than those in power diet groups ([470.4±2.7], [494.3±2.9], [512.3±5.7] mm, respectively) (P<0.05). At 6 weeks, there were more mRNA expressions of Notch-3, Jagged-1 and Delta-like-1 in solid diet group than in power diet group (P<0.05). The Notch-1 protein could be found in all layers of condylar cartilage, especially in the surface of hypertrophic zone. The expressions of Notch-1, Notch-3, and Delta-like-1 protein were increased from 2 to 6 weeks, and decreased at 8 weeks. In solid diet groups, the protein expressions of Notch-1 (at 2, 4, 6, 8 weeks), Notch-3 (at 2, 4, 6 weeks), Jagged-1 (at 2, 4, 6 weeks) and Delta-like-1 (at 4, 6, 8 weeks) were greater than in power diet groups (P<0.05). Conclusions: Low masticatory loading may delay or inhibit the development of condylar cartilage and its growing factors such as Notch-1, Notch-3, Jagged-1 and Delta-like-1. Appropriate masticatory loading plays an important role in normal development of the condyle.