The specific JNK inhibitor SP600125 targets tumour necrosis factor-α production and epithelial cell apoptosis in acute murine colitis

Stress-activated protein kinases (SAPKs) are activated in human inflammatory bowel disease (IBD). Recently it has been demonstrated that p38MAPK (mitogen-activated protein kinase) inhibition using SB203580 is effective in reducing disease in both dextran sulphate sodium (DSS)-induced and 2,4,6-trinitrobenzenesulphonic acid (TNBS)-induced murine colitides, underscoring the importance of this pathway in gastrointestinal inflammation. However, the contribution of c-Jun N-terminal kinase (JNK) in intestinal inflammation is unknown. Based on the known involvement of JNK in tumour necrosis factor-α (TNF-α) expression and in mediating the effects of oxidant stress, we hypothesized that JNK inhibition would also affect colitis. Our studies in mice with DSS-induced colitis treated with the JNK inhibitor SP600125, indicate that there is a significant reduction in wasting as well as a significant reduction in histological damage scores. Both total colonic and mesenteric lymphocyte CD3/CD28-stimulated TNF-α levels were dramatically reduced under the same circumstances. This was associated with a reduction in JNK protein expression and activity, as well as a reduction in AP-1 DNA binding with SP600125. Interestingly, there were no apparent changes in either p38MAPK or p42/44ERKs. Immunofluorescence of the colon for the active form of JNK revealed a prominent signal arising from the infiltrating inflammatory cells. SP600125 reduced this as well as, specifically, macrophage infiltration. Strikingly, we also demonstrate reduced epithelial cell apoptosis in response to treatment with SP600125. We conclude that specific inhibition of JNK is beneficial in the DSS model of colitis, and may be of value in human IBD

Signal transduction by the lipopolysaccharide receptor, Toll-like receptor-4

An understanding of lipopolysaccharide (LPS) signal transduction is a key goal in the effort to provide a molecular basis for the lethal effect of LPS during septic shock and point the way to novel therapies. Rapid progress in this field during the last 6 years has resulted in the discovery of not only the receptor for LPS – Toll-like receptor 4 (TLR4) – but also in a better appreciation of the complexity of the signalling pathways activated by LPS. Soon after the discovery of TLR4, the formation of a receptor complex in response to LPS, consisting of dimerized TLR4 and MD-2, was described. Intracellular events following the formation of this receptor complex depend on different sets of adapters. An early response, which is dependent on MyD88 and MyD88-like adapter (Mal), leads to the activation of nuclear factor-κB (NF-κB). A later response to LPS makes use of TIR-domain-containing adapter-inducing interferon-β (TRIF) and TRIF-related adapter molecule (TRAM), and leads to the late activation of NF-κB and IRF3, and to the induction of cytokines, chemokines, and other transcription factors. As LPS signal transduction is an area of intense research and rapid progress, this review is intended to sum up our present understanding of the events following LPS binding to TLR4, and we also attempt to create a model of the signalling pathways activated by LPS