Fig. 3

Degenerative IVD shares a close association with increased NP cell senescence. a SA-β-gal staining images of senescent NP cells in normal IVD and degenerative IVD under a microscope (× 400); dark blue-stained cells were senescent ones. b The positive rate of SA-β-gal staining in normal IVD and degenerative IVD; the positive rate of SA-β-gal staining represents the percentage of dark blue-stained NP cells in total NP cells; the experiment was repeated three times independently; data were expressed by mean ± standard deviation; comparison of data between two groups was conducted using a t-test; *, p < 0.05 vs. normal IVD; IVD, intervertebral disc; NP, nucleus pulposus; SA-β-gal, senescence-associated β-galactosidase