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

Introduction The aim of this study was to compare the effects of tumour necrosis factor-alpha (TNF-alpha) and interleukin-1-beta (IL-1 beta) on protease and catabolic cytokine and receptor gene expression in normal and degenerate human nucleus pulposus cells in alginate culture. Methods Cells 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-alpha or IL-1 beta for 48 hours prior to RNA extraction. Quantitative real-time polymerase chain reaction was used to assess the effect of TNF-alpha or IL-beta stimulation on the expression of matrix metalloproteinase (MMP)-3, -9 and -13, TNF-alpha, TNF receptor 1 (TNF-R1), TNF receptor 2 (TNF-R2), IL-1 alpha, IL-1 beta, IL-1 receptor 1 (IL-1R1) and IL-1 receptor antagonist (IL-1Ra). Results MMP-3 and MMP-9 gene expressions were upregulated to a greater level by IL-1 beta than TNF-alpha. MMP-13 was upregulated by each cytokine to a similar extent. TNF-alpha and TNF-R2 expressions were upregulated by both TNF-alpha and IL-beta, whereas TNF-R1 expression was not significantly affected by either cytokine. IL-1 beta and IL-1Ra expressions were significantly upregulated by TNF-alpha, whereas IL-1 alpha and IL-1R1 were unchanged. Conclusions TNF-alpha does not induce MMP expression to the same degree as stimulation by IL-1 beta, but it does act to upregulate IL-1 beta expression as well as TNF-alpha 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-alpha may be an important initiating factor in matrix degeneration, IL-1 beta plays a greater role in established pathological degradation.