Murine Studies on the Impact of TIM3 on Inflammatory Bowel Disease: Characterization, Mechanisms and Modulation

Background and aims: Inflammatory bowel disease (IBD) and its two main sub-groups, Crohn’s disease and ulcerative colitis, are chronic disorders affecting the gastro-intestinal tract. Although research progressed substantially over the past years and numerous therapeutic options for IBD treatment emerged, a considerable number of patients fail to react sufficiently to existing drugs or become non-responders eventually. Hence, there is a need to continuously develop new therapies, which simultaneously implies the necessity to further decipher the underlying mechanisms of IBD. In this regard, the T cell immunoglobulin and mucin domain receptor TIM3 may be a promising new target. Besides its role in cancer immunity, it has also been reported to have an immunosuppressive impact in IBD. The aim of this study was to evaluate the role of TIM3 in murine experimentally induced colitis and to gain new insights into intracellular mechanisms linked to TIM3 signalling. Methods: In this study, both in vitro and in vivo techniques were utilized. Oxazolone was used to induce experimental colitis. Gene expression patterns were assessed via quantitative PCR in whole colon tissue and isolated lamina propria mononuclear cells (LPMCs) from mice treated with oxazolone or healthy controls. TIM3 was stained in colonic tissue slides using immunofluorescence stainings. TIM3-deficient mice were studied under healthy and inflammatory conditions employing mini-endoscopy, flow cytometry, immunofluorescence, or HE staining. Non-targeted metabolomic studies were conducted in LPMCs. Galectin 9, a natural ligand of TIM3, was administered as a possible treatment option for experimental colitis. Results: TIM3 was upregulated in the colon during inflammation and after T cell receptor stimulation. Mice lacking TIM3 displayed exacerbated oxazolone-induced colitis compared to wildtype controls accompanied by induced pro-inflammatory signalling. Metabolomic analysis uncovered a novel linkage of TIM3 with the purine degradation pathway in LPMCs. TIM3 KO mice showed a shift towards increased purine degradation and elevated levels of reactive oxygen species. Subsequent analysis revealed that TIM3 might modulate adenosine deaminase activity, an enzyme initiating purine degradation. Moreover, treatment with Galectin 9 ameliorated chronic experimental colitis but is also associated with lethal side-effects at higher dosages. Conclusion: This is the first study connecting TIM3 with metabolic processes, especially purine metabolism, in a murine model of inflammatory bowel disease. Collectively these data presented important novel insights into TIM3 signalling and its crucial role in facilitating the resolution of inflammation during colitis. Thus, TIM3 is an interesting target for future IBD therapies.