Fig. 4

The effect of receptor activator of nuclear factor kappa B ligand (RANKL) on the mRNA expression of matrix-degrading enzymes and proinflammatory cytokines with or without recombinant human interleukin-1 beta (rhIL-1β) stimulation. The mRNA expression of IL-1β (a, b), matrix metalloprotease (MMP)-3 (c, d), and MMP-13 (e, f) by annulus fibrosus (AF) (a, c, e) and nucleus pulposus (NP) (b, d, f) cells were quantified by real-time polymerase chain reaction. The mRNA expression levels of MMP-3 by AF cells and those of MMP-13 by both AF and NP cells were significantly upregulated by stimulation of rhRANKL with rhIL-1β (1.0 ng/mL). Similar, but not significant trends were also identified in the expression level of IL-1β by both AF and NP cells, and that of MMP-3 by NP cells: *p < 0.05, **p < 0.01