Inhibiting IL-1 Signaling Pathways to Inhibit Catabolic Processes in Disc Degeneration

Intervertebral disc degeneration is characterized by an imbalance between catabolic and anabolic signaling, with an increase in catabolic cytokines particularly IL-1 beta, a key regulator of IVD degeneration. This study aimed to investigate intracellular signaling pathways activated by IL-1 beta, and GDF-5 in the degenerate IVD to identify potential new therapeutic targets. Human NP cells were cultured in alginate beads to regain in vivo phenotype prior to stimulation with IL-1 beta or GDF-5 for 30 min, a proteasome profiler array was initially utilized to screen activation status of 46 signaling proteins. Immunoflourescence was used to investigate activation of the NF kappa B pathway. Cell-based ELISAs were then deployed to confirm results for ERK1/2, p38 MAPK, c-jun, and I kappa B signaling. IHC was utilized to investigate native activation status within human IVD tissue between grades of degeneration. Finally, cells were stimulated with IL-1 beta in the absence or presence of p38 MAPK, c-jun, JNK, and NF kappa B inhibitors to investigate effects on MMP3, MMP13, IL-1 beta, IL-6, and IL-8 mRNA expression. This study demonstrated three key signaling pathways which were differentially activated by IL-1 beta but not GDF-5; namely p38 MAPK, c-jun, and NF kappa B. While ERK 1/2 was activated by both GDF-5 and IL-1. Immunohistochemistry demonstrated p38 MAPK, c-jun, and NF kappa B were activated during human IVD degeneration and inhibition of these pathways reduced or abrogated the catabolic effects of IL-1 beta, with inhibition of NF kappa B signaling demonstrating most widespread inhibition of IL-1 beta catabolic effects. (C) 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.