Collagen Synthesis and Types I, III, IV, and VI Collagens in an Animal Model of Disc Degeneration

Study Design. The present study sought to elucidate the changes that occur in collagen chemistry in the early phases of disc degeneration. Objective. To monitor the healing process of the injured anulus fibrosus and the secondary degenerative reactions in the nucleus pulposus. Summary of Background Data. Despite the importance of collagen chemistry under pathologic conditions in the intervertebral disc, knowledge of this aspect is very limited. Methods. Fourteen pigs were stabbed with a scalpel blad in the anterior part of the anulus fibrosus of a lumbar disc. The animals were killed 2 weeks to 5 months after injury. The activities of prolyl 4-hydroxylase adn galactosylhydroxylysyl glucosyltransferase, the total collagen content, adn staining patterns for Types I, III, IV, and VI collagens were analyzed from different parts of the disc. Results. The most active phase of the healing process, assessed from the activities of enzymes involved in collagen biosynthesis, took place during the first month postoperatively. The anular lesion was found to cicatrize through formation of disorganized granulation tissue in which Type I, III, and, IV collagens were depostited. In the nucleus pulposus, activities of pralyl 4-hydroxylase and galactosylhydroxylysyl glucosyltransferase and total collagen content increased, and the originally rounded cells became more elongated, resembling fibroblasts. Conclusions. The results of this study suggest that the altered composition of collagens observed in the degenerate porcine nucleus pulposus results from changes in cell phenotype: Notochondral cells were replaced by fibroblast-like cells. It is likely that trauma to the anulus fibrosus can initiate a progressive degenerative process in the disc tissue.