Effect of tumor necrosis factor-alpha, interleukin-1beta, and limited nutrition on matrix metalloproteinase (MMP)-9 and MMP-13 expression. Expression analysis of MMP-9 and MMP-13 mRNA in nucleus pulposus (NP) (A) and annulus fibrosus (AF) (B) tissues after the treatment. Both MMP-9 and MMP-13 are significantly upregulated after the treatment. Results are shown as the mean ± standard error for three independent experiments (n = 6 discs/group per experiment). *P <0.05. Western blot analysis of MMP-9 (C) and MMP-13 (D) in NP and AF tissue lysates after 3 days in culture. The expression of MMP-9 (E) and MMP-13 (F) is increased in the treated samples. Ctr., control group; Exp, experimental group.