Inhibition of RICK/Nuclear Factor-κB and p38 Signaling Attenuates the Inflammatory Response in a Murine Model of Crohn Disease

Abstract

Nuclear factor-B (NF-B) is the main target of antiinflammatory therapies in human chronic inflammatory bowel diseases (IBD), Crohn disease, and ulcerative colitis. This study investigates the molecular anti-inflammatory mechanisms of SB203580, an inhibitor of the mitogen-activated protein kinase p38. The murine trinitrobenzene sulfonic acid (TNBS)-induced colitis was used as an established model of human Crohn disease. Here we show that SB203580 improved the clinical condition, reduced intestinal inflammation, and suppressed mRNA levels of pro-inflammatory cytokines elevated upon induction of colitis. Besides p38 kinase activity, the "classical" I B-dependent NF-B pathway was strongly up-regulated during colitis induction, whereas the "alternative" was not. SB203580 treatment resulted in a drastic down-regulation of p38 and NF-B activity. The molecular analysis of NF-B activation revealed that Rip-like interacting caspase-like apoptosis-regulatory protein kinase (RICK), a key component of a pathway leading to NF-B induction, is also strongly inhibited by SB203580. In contrast, SB203580 had no effect on the colitis-induced activation of other potential NF-Bactivating kinases such as protein kinase C (PKC ), mixed lineage kinase 3, and the oncogene product Cot/ TPL2. Thus, the inhibitory effect of SB203580 on NF-B activation is to a large extent mediated by RICK inhibition. RICK is the effector kinase of the intracellular receptor of bacterial peptidoglycan NOD. Because bacterial products are suggested to be the key pathogenic agents triggering IBD, inhibition of the NOD/RICK pathway may serve as a novel target of future therapies in human IBD.Crohn disease is characterized by chronic intestinal inflammation frequently relapsing with clinical manifestations including diarrhea, blood in the stool, abdominal pain, and weight loss. The etiology of Crohn disease is so far unknown (1) but epidemiological and linkage studies suggest a genetic predisposition of the patient and the involvement of environmental factors (1, 2). Furthermore, several observations strongly implicate a pathogenic role of the intestinal flora during the initiation process of the immunological dysregulation (3-5).

Mitogen activated protein kinases: a role in inflammatory bowel disease?

“…By directly binding and phosphorylating transcription factors including the peroxisome proliferatoractivated receptor alpha [12] (which has been shown in a mouse model to be anti-inflammatory [41] and thus offers a possible explanation as to the conflicting data surrounding the claim that p38 is proinflammatory; see later) and Cdx-2, which has been shown during colonocyte cell line and intestinal epithelial cell differentiation [42], p38 can directly induce inflammatory gene transcription. Further studies using induction of IBD or infection with a nematode to induce an inflammatory response have substantiated a role in p38 regulating genes involved in the innate immune response by the gastrointestinal tract [43,44]. Similarly, indirect phopshorylation of various proteins can affect the activation of transcription factors, arguably one of the most important being NFkB, which was shown in an in vivo mouse model simulating IBD, to be subject to regulation via p38 [36].…”

“…These studies have investigated various cell types (both primary and cultured), including monocytes, colonocytes and myofibroblasts, but also include a host of animal studies where IBD-like inflammation was induced. Through the signalling pathways outlined previously, inflammatory responsesmainly cytokine production and inflammatory cell infiltration -have been shown to be attenuated by usage of specific inhibitors against p38 and JNK [27,35,38,44,52,63].…”

“…These studies can possibly be reconciled with the other contradictory data as being due to different experimental set-ups. For example, a difference in the administration of the chemical-inducing agent is evident, and also the time during which the experiments were performed [44,65]. Similarly, controversy also surrounds the role that JNK 1/2 plays in IBD.…”

Insights from advances in research of chemically induced experimental models of human inflammatory bowel disease

“…It has been demonstrated that IL-12p40 KO mice develop severe TNBS-induced colitis. Moreover, administration of IL-12p40 neutralizing antibody increases pathology in IL12p35 KO mice, which suggests that IL-12p40, in contrast Pathogenic factors Categories Factors (References) T cells Th1 [8] , CD8 + TCR Vβ14 + T cell [21] , CEACAM1 [27] Cytokines/chemokines IL-12 [8,30] , IFN-γ [8,34] , IL-18 [31,32,139] , IL-6 [73] , IL-16 [140] , IL-17 [38] , TNF-α [29,141] , MIP-α [142] , MIP-3α [143] Receptors CD40 [57,58] , CD44v7 [144] , FcεRI [145] , GITR [63,64] , Complement receptor 3 [146] Transcription factors NF-κB p65 [65,67,147] , RICK [69,70] , MAPK p38 [70] , Smad7 [72] , Smad3 [148] Adhesion molecules Integrinα1β1 [80] Enzymes Poly (ADP-ribose) synthetase [149,150] , Inducible nitric oxide synthase [151] , Angiotensinogen [152] , Vanin-1 [107] Hormones Leptin [113] , Ghrelin [153] , Adiponectin [112] Others Geneticfactors [11] , Glycolipid [154] Regulatory factors Categories Factors (References) T cells TCRγδ …”

“…In addition to NF-κB, mitogen-activated protein kinase (MAPK) p38 is also a crucial mediator of inflammation. Inhibition of NF-κB and MAPK p38 by SB203580 is able to attenuate the inflammatory response in TNBS-induced colitis models [69,70] . By contrast, TGF-β1 functions as a negative regulator of T-cell immune responses, signaling target cells through the Smad family of proteins.…”