Abstract:

BACKGROUND: Hypoxia-inducible factor 1 α is highly correlated with normal physiology and pathology of intervertebral disc cartilage because it can maintain normal activities of cartilage in hypoxia. After knockout of hypoxia-inducible factor 1α, cartilage cannot maintain the hypoxia state, resulting in nutritional disturbance, and hypoxia/ischemia in chondrocytes. Consequently, cartilage degeneration occurs.
OBJECTIVE: To observe the degeneration of intervertebral disc cartilage end-plate in hypoxia-inducible factor 1α gene knockout mice and investigate the effects of Chinese herbal compound Yiqihuayu Prescription on intervertebral disc cartilage end-plate degeneration.
METHODS: We collected 2.5- (n=6) and 4.5-month-old (n=6) hypoxia-inducible factor 1α gene knockout mice and wild type hypoxia-inducible factor 1α^+/+ control mice were obtained by interbreeding. The mice were sacrificed at 2.5 and 4.5 months old. Lumbar vertebra at L_4-6 levels was harvested for Safranin O/fast green, hematoxylin-eosin, immunohistochemical staining. Another 12 hypoxia-inducible factor 1α gene knockout mice of 0.5 month old were randomly assigned to normal saline and Yiqihuayu Prescription groups. Following intragastrical administration for 2 months, lumbar vertebra at L_4-6 levels was harvested for Safranin O/fast green, hematoxylin-eosin, immunohistochemical staining and analysis.
RESULTS AND CONCLUSION: For hypoxia-inducible factor 1α^-/- mice, mice at 2.5 months old developed aging related cartilage loss and bony tissue appearance, in addition to cartilage defects, uneven distribution of cells, and chondrocyte reduction. In addition, type II collagen and Sox-9 expression in intervertebral disc cartilage decreased, while type X collagen and matrix metalloproteinase 13 expression increased. At 4.5 months old, the cartilage injury was worsened, type II collagen and Sox-9 expression further reduced, and type X collagen and matrix metalloproteinase 13 expression further increased. Compared with normal saline group, Yiqihuayu Prescription reduced ossification and defect of endplate cartilage, the number of chondrocytes increased, and the distribution was more uniform as shown by Safranin O/fast green and hematoxylin-eosin staining. Moreover, Yiqihuayu Prescription increased type II collagen and Sox-9 expression, but decreased type X collagen and matrix metalloproteinase 13 protein expression. The results indicate that intervertebral disc cartilage degeneration occurred in hypoxia-inducible factor 1α gene knockout mice, which was progressed with aging of mice. Yiqihuayu Prescription can attenuate the degeneration of intervertebral disc cartilage in hypoxia-inducible factor 1α gene knockout mice.

Key words: tissue construction, tissue construction and bioactive factors, Yiqihuayu Prescription, hypoxia-inducible factor 1α, gene knockout mice, intervertebral disc, cartilage, degeneration, ossification, bone defect, type II collagen, chondrocyte, matrix metalloproteinase, National Natural Science Foundation of China