Regulation of catabolic gene expression in normal and degenerate human intervertebral disc cells: implications for the pathogenesis of intervertebral disc degeneration

IntroductionThe aim of this study was to compare the effects of tumour necrosis factor-alpha (TNF-α) and interleukin-1-beta (IL-1β) on protease and catabolic cytokine and receptor gene expression in normal and degenerate human nucleus pulposus cells in alginate culture.MethodsCells isolated from normal and degenerate nucleus pulposus regions of human intervertebral discs were cultured in alginate pellets and stimulated by the addition of 10 ng/mL TNF-α or IL-1β for 48 hours prior to RNA extraction. Quantitative real-time polymerase chain reaction was used to assess the effect of TNF-α or IL-β stimulation on the expression of matrix metalloproteinase (MMP)-3, -9 and -13, TNF-α, TNF receptor 1 (TNF-R1), TNF receptor 2 (TNF-R2), IL-1α, IL-1β, IL-1 receptor 1 (IL-1R1) and IL-1 receptor antagonist (IL-1Ra).ResultsMMP-3 and MMP-9 gene expressions were upregulated to a greater level by IL-1β than TNF-α. MMP-13 was upregulated by each cytokine to a similar extent. TNF-α and TNF-R2 expressions were upregulated by both TNF-α and IL-β, whereas TNF-R1 expression was not significantly affected by either cytokine. IL-1β and IL-1Ra expressions were significantly upregulated by TNF-α, whereas IL-1α and IL-1R1 were unchanged.ConclusionsTNF-α does not induce MMP expression to the same degree as stimulation by IL-1β, but it does act to upregulate IL-1β expression as well as TNF-α and TNF-R2. The net result of this would be an increased inflammatory environment and accelerated degradation of the matrix. These results support the hypothesis that, while TNF-α may be an important initiating factor in matrix degeneration, IL-1β plays a greater role in established pathological degradation.