IL-1Ra deficiency accelerates intervertebral disc degeneration in C57BL6J mice

Abstract

The expression of Interleukin-1ß (IL-1ß) and its antagonist and Interleukin-1 receptor antagonist (IL-1Ra) are correlated with greater human intervertebral disc (IVD) degeneration, suggesting that elevated IL-1β activity promotes disc degeneration. Many in vitro studies support such a mechanistic relationship, whereas few in vivo investigations have been reported. The present study tests the effect of increased IL-1β activity on intervertebral disc in mice with an IL-1Ra gene deletion. IL-1Ra−/− mice and wild-type (WT) C57Bl6J mice were examined at 3 and 12 months of age. Caudal IVD segments were evaluated for disc degeneration by histopathology, functional testing, and inflammatory gene expression relevant to IL-1β pathways. To test differences in injury response, pinprick annular puncture was performed on IL-1Ra−/− and WT mice and evaluated similarly. IL-1Ra−/− IVDs had significantly worse histopathology at 3 months compared to WT controls, but not at 12 months. IL-1Ra−/− IVDs exhibited significantly more viscous mechanical properties than WT IVDs. qPCR revealed downregulation of inflammatory genes at 3 and 12 months in IL-1Ra−/− IVDs, with concomitant downregulation of anabolic and catabolic genes. Annular puncture yielded no appreciable differences between 2-week and 6-week post-injured WT and IL1-Ra−/− IVDs in histopathology or biomechanics, but inflammatory gene expression was sharply downregulated in IL-1Ra−/− mice at 2 weeks, returning by 6 weeks post injury. In the present study, IL-1Ra deletion resulted in increased IVD histopathology, inferior biomechanics, and transiently decreased pro-inflammatory cytokine gene expression. The histopathology of IL-1Ra−/− IVDs on a C57BL/6J background is less severe than a previous report of IL1Ra−/− on a BALB/c background, yet both strains exhibit IVD degeneration, reinforcing a mechanistic role of IL-1β signaling in IVD pathobiology. Despite a pro-inflammatory environment, the annular puncture was no worse in IL-1Ra−/− mice, suggesting that response to injury involves pathways other than inflammation. Overall, this study supports the hypothesis that IL-1β-driven inflammation is important in IVD degeneration.