Preliminary research for correlation between BNIP3 expression and disc degeneration

English Keywords:Disc degeneration  Nucleus pulposus  BNIP3  Rabbit

English Abstract:

  【Abstract】 Objective：To study the correlation between BNIP3 expression and disc degeneration.Method：Twenty-four one-month white New Zealand rabbits were randomly and equally assigned into four groups：post-surgery for 0 week（n=6），post-surgery for 2 weeks（n=6），post-surgery for 4 weeks（n=6），and post-surgery for 8 weeks（n=6）.By puncturing the experimental disc annulus （L4/5，L5/6 and L6/7） with needle，we established a disc degeneration model in New Zealand white rabbit，the normal discs above the experimental discs（L1/2，L2/3 and L3/4） served as control.After the surgery for 0，2，4 and 8 weeks，the disc degeneration，BNIP3 expression and cell morphology were evaluated by using MRI，histochemistry staining，immunohistochemical staining and real-time-PCR，and the correlationship between the BNIP3 expression and the disc degeneration evaluated by MRI and histochemistry was also been analyzed.Result：The MRI showed that the normal discs and discs of post surgery for 0 week exhibited hyperintense in T2 weighting image with the average MRI grade of 1.0±0.0；the discs of post surgery for 2 weeks showed inhomogeneous hyperintense with the average MRI grade of 2.9±0.4；the discs of post surgery for 4 weeks showed intermediate to hypointense with the average MRI grade of 4.2±0.3；the discs of post surgery for 8 weeks showed a hypointense which the average MRI grade of 4.9±0.1.There were significant differences among normal discs and post surgery discs（P<0.05）.The histochemistry staining also showed the normal discs and discs of post surgery for 0 week with intact structure and clear border between the annulus fibrosus and nucleus pulposus，the average histological grade was 4.0±0.0；the discs of post surgery for 2 weeks showed slight rupture in annulus fibrosus and minimally interrupted between annulus fibrosus and nucleus pulposus，the average histological grade was 7.5±0.2；the discs of post surgery for 4 weeks showed larger rupture in annulus fibrosus and moderate rupture between annulus fibrosus and nucleus pulposus，the average histological grade was 10.0±1.0；the discs of post surgery for 8 weeks showed the collapse of disc structure and fibrosis of nucleus pulposus，the average histological grade was 11.8±0.2.There were significant differences among normal discs and post surgery discs（P<0.05）.The BNIP3 mRNA real-time-PCR of the nucleus pulposus region indicated increased expression of BNIP3 with 1.0±0.3-fold，2.0±0.1-fold，2.8±0.3-fold and 4.2±0.2-fold respectively at 0，2，4 and 8 weeks after surgery，and there was a high correlation between MRI grade and BNIP3 mRNA expression（r=0.92，P<0.01）.The BNIP3 immunohistochemical staining of the nucleus pulposus region suggested increased positive reaction with 150.4±13.4，176.0±35.1 and 173.6±7.9 of gray intensity at 2，4 and 8 weeks after surgery，which had a high correlation with histological grade（r=0.92，P<0.01）.Conclusion：The expression of BNIP3 mRNA has some relationship with the disc degeneration，and the increased expression of BNIP3 may play an important role in disc degeneration.