Purpose: Collagen production and reorientation are core events in the healing of tendons and are essential for gaining tensile strength. Intrasynovial flexor tendons are composed chiefly of type I collagen; however, type III collagen is the earliest to be laid down in the wounds. We investigated the expression of genes for type I collagen, type III collagen and its promoter, and nuclear transcription factor kappa B (NF-kappaB) in an in vivo tendon injury model in chickens.
Methods: Flexor digitorum profundus tendons of the long toes of 12 white leghorn chickens were transected partially and repaired with the modified Kessler method. The repaired tendon segments were harvested at 2, 4, and 8 weeks after surgery with 4 chickens used each time. The uninjured tendons from 4 other chickens were used as the controls. We determined the expression of the collagen and NF-kappaB genes in the tendons with reverse transcription and polymerase chain reaction and semiquantitative analysis of gene bands in gel electrophoresis.
Results: Expression of the type III collagen gene was enhanced significantly in the tendons at 2, 4, and 8 weeks after repair. Levels of expression of the type III collagen promoter gene were increased significantly in the healing tendons at 2 and 4 weeks. Increases in the expression of the type I collagen gene occurred later than those of the type III collagen and NF-kappaB genes and were significant in the tendons after 4 and 8 weeks. The NF-kappaB gene was activated in the tendons at all the healing periods.
Conclusions: Expression of type III collagen and its promoter genes is enhanced remarkably during in vivo flexor tendon healing. The NF-kappaB gene is activated during the healing process. Expression of the type I collagen gene increases remarkably at later periods of in vivo tendon healing and is proportional to that of the NF-kappaB gene.