TYPE-II COLLAGEN GENE-EXPRESSION IS TRANSIENTLY UP-REGULATED 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 rabbi ts and analyzed the level of expression of type-II collagen mRNA in di sc degeneration. An animal model was created by surgical denucleation of rabbit intervertebral discs through an extraperitoneal approach, Ei ght animals each from an experimental and a control group were killed al 2, 4, 8, or 16 weeks postoperatively: and the disc samples were use d for this study. Round chondrocyte-like cells that filled the herniat ed space showed intense signal of type-II collagen mRNA and significan t pericellular immunostaining of type-II collagen but no clear stainin g of type-I collagen. Northern blot analysis revealed that the express ion of type-II collagen mRNA of the repair disc cells was transiently increased at it weeks postoperatively, The cells were able to change t heir morphology in response to mechanical stimulation by surgical denu cleation and to induce a significant increase in the gene expression o f 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.