Type-II collagen gene expression is transiently upregulated in experimentally induced degeneration of rabbit intervertebral disc

To clarify phenotypic alterations of intervertebral disc cells during the repair process, we cloned partial type-II collagen cDNA from rabbits and analyzed the level of expression of type-II collagen mRNA in disc degeneration. An animal model was created by surgical denucleation of rabbit intervertebral discs through an extraperitoneal approach, Eight animals each from an experimental and a control group were killed al 2, 4, 8, or 16 weeks postoperatively: and the disc samples were used for this study. Round chondrocyte-like cells that filled the herniated space showed intense signal of type-II collagen mRNA and significant pericellular immunostaining of type-II collagen but no clear staining of type-I collagen. Northern blot analysis revealed that the expression of type-II collagen mRNA of the repair disc cells was transiently increased at it weeks postoperatively, The cells were able to change their morphology in response to mechanical stimulation by surgical denucleation and to induce a significant increase in the gene expression of type-II collagen at an early phase of disc degeneration. The present results indicate the transient enhancement of repair activity in the degenerative process of injured fibrocartilage.