| Background and objective:Articular cartilage injuries are frequent in clinic, but the repair of injuries is still an unsolved problem. Articular cartilage, that is hyaline cartilage, is avascular, alymphatic, insensate, and chondrocytes, deriving both oxygen and nutrition from the synovial fluid. It has a severely limited capacity to heal after the damage caused by injury or disease because of these structure characteristics.In a previous study, the morphologically good repairs with hyaline-like cartilage appearance were observed in young New Zealand rabbit after defect of articular cartilage in knee, but formation of fibrous tissue in adult rabbit. The different results of repair may imply the different repair mechanism. No matter what the repair mechanism is, it is critical for the repair of articular cartilage injuries to increase the synthesis of collagen and proteoglycan, and induce cell proliferation and differentiation. All these elements are obvious promoted by Growth factors.Connective tissue growth factor (CTGF) stimulated differentiation of mesenchymal stem cells towards chondrocytes, promoted proliferation and differentiation of chondrocytes and enhanced production of typeⅡcollagen and proteoglycan of rabbit chondrocytes. It had been proved that CTGF promoted regeneration of defects in articular cartilage in rat knee joints. Transforming growth factorβ1(TGF-β1) increased the synthesis of typeⅡcollagen and glycosaminoglycan, stimulated differentiation of mesenchymal stem cells towards chondrocytes and also promoted chondrocytes proliferation. But it is unknown whether or not the levels of expression of CTGF and TGF-β1 are significantly different during articular cartilage reapir after full-thickness cartilage defect in young and adult rabbits model.The purpose of present study was to observe macroscopic and histologic morphous of repairs and analyze the levels of expression of CTGF, TGF-β1 and typeⅡcollagen in articular cartilage after full-thickness cartilage defect on the medial femoral condyle in young and adult rabbits model, and to research the correlation between the quality of repair tissue and the levels of expression of CTGF and TGF-β1, therefore providing referenced evidence for repair mechanism of articular cartilage defect.Methods:25 young and 25 adult New Zealand white rabbits were randomly divided into five groups respectively(n=5): control group, 24 hour group, 1 week group,4 week group and 8 week group after injury. A rabbit model of spontaneous healing of full-thickness cartilage defect in the medial femoral condyle in both knees was produced in present study. Animals in each age group were killed at 24 hours, 1, 4 and 8 weeks. Macroscopic and histologic morphous (by hematoxylin/eosin staining, HE) of repairs were observed in each age group during repair. The mRNA and protein expression of CTGF, TGF-β1 and typeⅡcollagen were detected with RT-PCR and immunohistochemistry respectively. Levels of mRNA were measured by using semiquantitative RT-PCR as the proportion of individual RT-PCR product mean optical density toβ-actin RT-PCR product mean optical density of the same RNA sample. The data analysis was carried out with the SPSS13.0 software package. Statistical significance was set at P = 0.05.Results:At 1 week, the defects were not filled completely in both groups. At 4 weeks, more tissues were filled in all defects than they were at 1 week. Young rabbits showed more tissue regeneration than adult rabbits. At 8 weeks all defects in young group had been completely filled. The surface of the repair tissue appeared even, and it had a reddish color at 4 weeks and white at 8 weeks. While, in most instances, the defects were not filled completely in adult group.In terms of histologic observation, at 4 weeks, in no case did tissue regeneration reach the level of the surrounding cartilage. The repair tissue in young rabbits consisted mainly of fibrous tissue and incompletely differentiated mesenchyme, while in adult, mainly fibrous tissue. At 8 weeks, in young rabbits, the repairs were flush with the adjacent cartilage. Hyaline-like cartilage was found in young rabbits. In the adults, it was only a few instances and the regenerated tissue reached the level of the surrounding cartilage. The repair tissue was either fibrous tissue or incompletely differentiated mesenchyme.CTGF, TGF-β1 and typeⅡcollagen mRNA was continued expression during repairing of articrlar cartilage defect. Levels of CTGF mRNA, in young rabbit: A 0.350±0.014, B 0.719±0.012, C 0.864±0.010, D 0.442±0.009, E 0.438±0.010, in adult rabbit: A 0.119±0.009, B 0.509±0.011, C 0.519±0.009, D 0.348±0.010, E 0.227±0.008. Levels of TGF-β1 mRNA, in young rabbit: A 0.619±0.010, B 0.969±0.012, C 1.099±0.037, D 0.730±0.011, E 0.723±0.013, in adult rabbit: A 0.313±0.013, B 0.873±0.021, C 0.970±0.010, D 0.535±0.020, E 0.415±0.010. Levels of typeⅡcollagen mRNA, in young rabbit: A 0.604±0.005, B 0.813±0.005, C 1.091±0.006, D 0.650±0.002, E 0.741±0.002, in adult rabbit: A 0.039±0.004, B 0.195±0.004, C 0.604±0.006, D 0.095±0.005, E 0.087±0.003.Levels of expression of CTGF and TGF-β1 were significantly higher in all groups after defect than in control group in yong and adult rabbit (P<0.05).Levels of expression of CTGF, TGF-β1 and typeⅡcollagen mRNA were significantly higher in young rabbit than in adult rabbit (P<0.05).Levels of expression were positive correlation between CTGF and TGF-β1, between CTGF and typeⅡcollagen, and between TGF-β1 and typeⅡcollagen (P<0.05).The immunohistochemistry results showed that the expression of CTGF and TGF-β1 were positive in all groups.Conclusion:1. The repair tissue in young animals showed a better specialization of hyline cartilage than adult animals'.2. CTGF and TGF-β1 mRNA were continued expression during repairing of articrlar cartilage defect. Levels of expression of CTGF and TGF-β1 mRNA were significantly higher in all groups after defect than in control group. CTGF and TGF-β1 may play a role in the repair of articular cartilage defect.3. Levels of expression of CTGF and TGF-β1 mRNA were significantly higher in young rabbit than they were in adult rabbit during repair. The good specialization of repair tissue were accompanied with high expression of CTGF and TGF-β1 mRNA, which might be an important fact for good articrlar cartilage repair. Therefore, CTGF and TGF-β1 might improve the repair of articular cartilage defects in clinic. |
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