[Significance of BNIP3 gene expression and cell apoptosis in nucleus pulposus of degenerative intervertebral disc in rabbits].

OBJECTIVE: To detect the cell density, apoptotic rate, and the expressions of BNIP3 in nucleus pulposus of degenerative intervertebral disc of rabbits, so as to further understand the mechanism of intervertebral disc degeneration.

METHODS: Thirty male New Zealand white rabbits, aging 3 months and weighing (2.3 +/- 0.2) kg, were divided into sham operation group (control group, n = 10) and intervertebral disc degeneration model group (experimental group, n = 20). Intervertebral disc degeneration models were established by puncture of L3, 4, L4, 5, and L5, 6 intervertebral discs in the experimental group; intervertebral discs were exposed only and then sutured in the control group. The degree of intervertebral disc degeneration was evaluated according to Pfirrmann classification by MRI at 4 and 8 weeks after establishing models. Apoptotic cells were determined by TUNEL and histological methods, and the immunohistochemical staining was performed to detect the expressions of BNIP3 in nucleus pulposus of intervertebral disc.

RESULTS: MRI examination showed that the signal intensity decreased gradually at 4 and 8 weeks in the experimental group. There was significant difference in the degree of intervertebral disc degeneration between at 4 weeks and at 8 weeks in the experimental group (P < 0.05). The histological observation and TUNEL test showed that high density of nucleus pulposus cells and only a few apoptotic cells were observed in the control group; at 4 and 8 weeks, the density of nucleus pulposus cells decreased gradually with more apoptotic cells in the experimental group. There were significant differences in the nucleus pulposus cell density and positive rate of TUNEL staining between 2 groups, and between at 4 weeks and at 8 weeks in the experimental group (P < 0.05). The expression of BNIP3 of nucleus pulposus was negative in the control group; however, in the experimental group, the positive expression rates of BNIP3 of nucleus pulposus (the gray values) were 13.45% +/- 1.16% and 32.00% +/- 1.82% (194.32 +/- 4.65 and 117.54 +/- 2.11) at 4 and 8 weeks respectively, showing significant differences (P < 0.05).

CONCLUSION: The decrease of cell density in nucleus pulposus is involved in the development of intervertebral disc degeneration. Cell apoptosis is one of reasons in the decrease of nucleus pulposus cell; BNIP3 is involved in nucleus pulposus cell apoptosis in the degenerative intervertebral disc.