LAUSR

Interleukin 1 beta (IL-1β) is upregulated following a tendon injury and in vitro studies have shown that it leads to numerous negative effects on tendon cell function and gene expression. IL-1β activates nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and we hypothesised that inhibiting NF-κB activation would mediate the negative effects of IL-1β on equine tendon cells in 3-dimensional (3D) cultures. Here, we tested three inhibitors of NF-κB signalling (Bortezomib, BAY11-7082 and Wedelolactone) along withTJ-M2010-5, an inhibitor of MyD88, which is a critical adaptor protein for mediating IL-1β signalling. None of these inhibitors were able to rescue gel contraction by equine tenocytes exposed to IL-1β in 3D culture. However, the daily application of the interleukin-1 receptor-associated kinase (IRAK)−4 inhibitor PF-06650833 resulted in a partial rescue of collagen contraction and interleukin-6 (IL-6) production by equine tenocytes in 3D culture. Global gene expression using RNA sequencing also revealed a partial rescue, although this was not as complete as that achieved using interleukin-1 receptor antagonist protein (IL1Ra), with many inflammatory pathways remaining upregulated. ENPP2 expression was significantly increased by IL-1β and rescued by both IL1Ra and PF-06650833 suggesting ENPP2 may be involved in collagen contraction. However, direct ENPP2 inhibition does not rescue IL-1β mediated inhibition of contraction and ENPP2 inhibition alone reduces collagen contraction. Together, this data demonstrates that IL-1β has a broad mechanism of action on tendon cells which cannot be fully mediated by targeting specific parts of the signalling pathway.