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‐1β, a key regulator of IVD degeneration. This study aimed to investigate intracellular signaling pathways activated by IL‐1β, 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‐1β 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 NFκB pathway. Cell‐based ELISAs were then deployed to confirm results for ERK1/2, p38 MAPK, c‐jun, and IκB signaling. IHC was utilized to investigate native activation status within human IVD tissue between grades of degeneration. Finally, cells were stimulated with IL‐1β in the absence or presence of p38 MAPK, c‐jun, JNK, and NFκB inhibitors to investigate effects on MMP3, MMP13, IL‐1β, IL‐6, and IL‐8 mRNA expression. This study demonstrated three key signaling pathways which were differentially activated by IL‐1β but not GDF‐5; namely p38 MAPK, c‐jun, and NFκB. While ERK 1/2 was activated by both GDF‐5 and IL‐1. Immunohistochemistry demonstrated p38 MAPK, c‐jun, and NFκB were activated during human IVD degeneration and inhibition of these pathways reduced or abrogated the catabolic effects of IL‐1β, with inhibition of NFκB signaling demonstrating most widespread inhibition of IL‐1β catabolic effects. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:74–85, 2017.