Type I and type III procollagen gene expressions in the early phase of ligament healing in rabbits: an in situ hybridization study.

ABSTRACT

The purpose of this study is to observe type I and type III procollagen gene expressions in the healing ligament using in situ hybridization histochemistry. The rabbit medial collateral ligaments were incised and harvested at 3, 7, 14, and 28 days postoperatively. The healing ligament showed increased expression of both procollagen genes through this period compared with the unoperated ligament. The peak expression level was observed at 7 or 14 days for type I and at 7 days for type III, respectively. The strongest expression of both genes was detected in the scar tissue created between the ends of the old ligament. Although type III procollagen gene expression was observed almost only in the newly created scar tissue, type I procollagen gene was expressed not only in the scar tissue, but also at the ends of the previously normal ligament. These results suggest that type I collagen synthesis begins shortly after ligament injury and occurs at the ends of the injured ligament as well as in the scar tissue, and that type III collagen is largely synthesized in the scar tissue around one week after injury but continues being synthesized for at least four weeks after injury.