Abstract: BACKGROUND: Fragments of articular cartilage can enhance bone repair ability, the specific mechanism of which is still unclear.  
OBJECTIVE: To investigate the relationship between transforming growth factor β1 (TGF-β1) expression and chondrocyte migration in adult fragmented articular cartilage.
METHODS:  Hind limbs (60 knees) from 30 male Sprague-Dawley rats of 12-15 weeks old, SPF grade, were aseptically collected, and the articular cartilage particles (about 1 mm × 1 mm × 1 mm) and massive cartilage blocks (approximately 5 mm in diameter and 2 mm in thickness) were obtained by cross-cutting method. In vitro culture model of composite gelatin sponge crumb and fibrin glue was established. There were three experimental groups: fragment group, whole block group, and inhibitor group. Both the fragment group and the whole group were cultured in a common cell culture medium, and the inhibitor group was treated with an exogenous TGF-β1 inhibitor, Decori, and a common cell culture solution. Transwell assay was used to detect cell migration. Phalloidin staining was used to observe the change of F-actin. The expression of TGF-β1 mRNA and protein was detected by qRT-PCR and western blot, respectively. Molecular docking technique was used to explore the relationship between TGF-β1 and F-actin.  
RESULTS AND CONCLUSION: Transwell assay results showed that the number of cells passing through matrigel increased significantly in the fragment group compared with the whole block group (P < 0.05). Compared with the fragment group, the number of cells passing through matrigel in the inhibitor group was significantly reduced (P < 0.05). The phalloidin staining results indicated that the F-actin ring structures were significantly reduced in the fragment group compared with the whole block group. Filamentous structures gradually formed with stress fibers in the cells being significantly reduced, the intercellular space beining significantly reduced, and cartilage damage recovering gradually. Compared with the fragment group, the F-actin ring structures were significantly increased in the inhibitor group, presenting with the intercellular space evidently enlarging. Compared with the whole block group, the expression levels of TGF-β1 mRNA and protein increased significantly in the fragment group (P < 0.05); compared with the fragment group, the expression levels of TGF-β1 mRNA and protein decreased significantly in the inhibitor group (P < 0.05). In the molecular docking simulation, TGF-β1 was combined with F-actin to form a stable complex, which was mainly based on hydrogen bonding force. Findings from this study indicate that TGF-β1 can overexpress in adult fragmented articular cartilage, and the overexpression of TGF-β1 can promote chondrocyte migration and promote cartilage.

Key words: transforming growth factor-β1, articular cartilage, fragment, chondrocyte migration, F-actin, transforming growth factor β1 inhibitor