S1731 Tolerance of Toll-Like Receptor 4 Mediated Signaling Pathway Protects Mice from Experimental Colitis

Abstract

Background:The basis of inflammatory bowel disease (IBD) is multi-factorial involving susceptibility genes, and immune and environmental factors. There has been a rapid increase in the prevalence of IBD in industrialized countries. The hygiene hypothesis proposes that the present clean surroundings in less exposure to bacteria are involved in development of this disease. Toll-like receptor (TLR) 4 agonist, lipopolysaccharide (LPS), has a phenomenon termed LPS tolerance such as an initial exposure to LPS induce a transient state of hyporesponsiveness to a subsequent challenge with LPS. Based on In Vitro studies, the mechanisms of this phenomenon are gradually becoming clear, although that has not been formally proven in inflammatory disease models In Vivo. Therefore we hypothesized that repeated LPS administration could protect colonic inflammation of mouse experimental colitis model. Methods:Murine colitis was induced to Balb/c mice by oral administration of 7% dextran sulphate sodium (DSS) with or without daily intraperitoneal administration of LPS. Colitis was evaluated by a macroscopic disease activity index, myeloperoxidase (MPO) activity in colon and histological score. Cytokine mRNA expressions in colon were also measured by RT-PCR. To confirm the phenomenon of LPS tolerance, we generated mouse conventional bone marrow derived dendritic cells (BMDC), and these were preincubated with or without LPS and restimulated with LPS after 24 hours from first stimulation. Cytokine productions in the culture supernatant were measured by ELISA, and mRNA expressions of the cells were evaluated by RT-PCR. Furthermore, we investigated negative regulators of LPS tolerance and expression of them in model of experimental colitis. Results:Administration of LPS significantly suppressed colonic inflammation of DSS-induced colitis, although there were no difference in mRNA expression of IL-12p40, IL-6, TNF-α, IL-10, and TLR4. TLR4 in BMDC was activated with LPS and induced TNF-α production. After second stimulation with LPS, TNF-α and IL-6 production were reduced which followed previous reports. IRAKM mRNA expression, which had participation in LPS tolerance, was upregulated in the LPS treated BMDC and mice colon in comparison to the control mice. Conclusion:LPS tolerance could protect mice from DSS-induced colitis, and IRAK-M had participation in LPS tolerance of TLR4 signaling pathway. Taken together, these observations suggested that loss of exposure to LPS may be one of the pathogenesis of IBD.