Age- and injury-dependent concentrations of transforming growth factor- β1 and proteoglycan fragments in rabbit knee joint fluid

Abstract

Objective: The purpose of the study was to characterize maturation- related changes of TGF-β1 and proteoglycan fragment (PG) concentrations in joint fluid of healthy rabbit knees, and to investigate changes associated with osteochondral injury and spontaneous repair. Methods: In 26 young (age range: 12-15 weeks), 26 adolescent (18-25 weeks), and 26 adult (33-44 weeks) New Zealand white rabbits, TGF-β1 and PG concentrations were analyzed in joint fluid samples which were taken before, and at several time intervals (max. 1 year) after creation of a osteochondral defect in the knee medial femoral condyle. At death, the characteristics of the regenerated tissue in the defect and any signs of degeneration of adjacent cartilage were recorded and graded. Results: In preoperative samples, TGF-β1 and PG concentrations decreased with maturation (P < 0.01), and were moderately correlated (r = 0.51, P < 0.001). Shortly after trauma, the concentrations of both substances were found increased, which was followed by a decrease up to 3 months, and then again an increase up to 1 year. However, meanwhile PG concentrations had similar magnitude irrespective of age, TGF-β1 concentrations never reached similarly high levels in adulthood as an infancy or adolescence. The cartilage adjacent to the defect had more signs for degeneration in younger rabbits, and also osteophytes were more common in young than adult animals. Conclusion: The similar pattern for TGF-β1 and PG concentrations during postnatal maturation may reflect the stimulatory effect of TGF-β1 on proteoglycan synthesis. The higher TGF-β1 concentrations in younger animals may be a reason for their better healing capacity, but also for their higher susceptibility to osteoarthritic change compared to adult animals.