Abstract:

BACKGROUND: Studies have shown that the changes of extracellular matrix in degenerative intervertebral disc tissues mainly present as the decrease of collagen type Ⅱ and proteoglycan contents and the increase of collagen type Ⅰ content.
OBJECTIVE: To explore the effect of adeno-associated virus-mediated bone morphogenetic protein 2 gene on nucleus pulposus Ⅰ and Ⅱ collagen levels in rabbit degenerative intervertebral disc tissues.
METHODS: L2-3, L3-4, L4-5 and L5-6 lumbar discs of 12 New Zealand white rabbits were punctured to establish interverbral disc degeneration model. Subsequently, 12 rabbits were randomly divided into three groups, four rabbits in each group. The intervertebral discs in the adeno-associated virus-mediated bone morphogenetic protein 2 group were injected with the adeno-associated virus-mediated bone morphogenetic protein 2 gene, the intervertebral discs in the adeno-associated virus group were injected with adeno-associated virus only, while the discs in the normal saline group were injected with normal saline. All rabbits were sacrificed after injected for 8 weeks, and the L2-3, L3-4, L4-5 and L5-6 lumbar discs of each rabbit were collected, paraffin-embedded and sliced. The histological changes of nucleus pulposus were observed with hematoxylin-eosin staining, and the immunohistochemistry was used to detect the collagen type Ⅰ and Ⅱ expressions in nucleus pulposus. Semi-quantitative analysis was performed.
RESULTS AND CONCLUSION: Hematoxylin-eosin staining showed that the nucleus pulposus in the intervertebral disc tissues was less in the adeno-associated virus-mediated bone morphogenetic protein 2 group, the nucleus pulposus was in single or clustered distribution with clear nucleus structure and without fibrous tissue filling. The tissue structures of nucleus pulposus were the same in the adeno-associated virus group and normal saline group, the cell number in nucleus pulposus was small, the nucleus pulposus was shrunken and shriveled, and the cells were filled with fibrous tissue and arranged disorderly. Immunohistochemistry staining showed the expression of collage type Ⅰ in the intervertebral disc nucleus pulposus of adeno-associated virus-mediated bone morphogenetic protein 2 group was higher than that of the adeno-associated virus group and normal saline group (P < 0.05); the expression of collage typeⅠ in the intervertebral disc nucleus pulposus of adeno-associated virus-mediated bone morphogenetic protein 2 group was lower than that of the adeno-associated virus group and normal saline group (P < 0.05). The results indicate that adeno-associated virus-mediated bone morphogenetic protein 2 can inhibit the expression of collagen type Ⅰ in the intervertebral disc nucleus pulposus, promote the expression of collagen type Ⅱ. Maintaining the content of collagen in intervertebral disc can keep the histological structure and morphology of intervertebral disc, stabilize the environment for nucleus pulposus cell growth, and delay the intervertebral disc degeneration.

Key words: bone morphogenetic proteins, intervertebral disk, collagen type Ⅰ, collagen type Ⅱ