Role of cytokine IL-15 in the homeostasis of the intestinal epithelium and inflammatory bowel diseases

Inflammatory bowel diseases (IBD), such as Ulcerative Colitis and Crohn’s disease, are characterized by increased intestinal permeability caused by intestinal mucosal barrier dysfunction, a critical factor in the pathogenesis of IBD. The immune system is the major effector of this tissue damage, through the action of multiple cell types as well as soluble mediators, such as TNFα, which are currently therapeutic targets in the treatment of IBD. Interleukin 15 (IL-15) is a pro-inflammatory cytokine involved in maintenance and activation of subgroups of cytotoxic lymphocytes and macrophages in the intestinal epithelium, by acting through the 3-subunit receptor IL-15R. IL-15 receptor complex consists of a unique IL-15R alpha subunit, IL-2/IL-15R beta, and the common gamma-chain/IL-2R gamma subunit. IL-15 expression is increased in IBD and in murine models of intestinal inflammation. However, the exact role of IL-15 signaling in intestinal homeostasis and inflammatory responses, particularly in intestinal epithelial cells (IEC), remains to be determined. The function of IL-15 has been widely described in immune cells, but its functions in other tissues are less well known. The aim of this thesis is to investigate the role of IL-15 in the homeostasis of the intestinal epithelium and in inflammatory bowel diseases. We tested the influence of IL-15 on intestinal homeostasis in C57BL/6 wild-type (WT), IL-15 deficient (Il15-/-) and IL-15R[alpha] deficient (Il15ra-/-) mice. After 7 days, macromorphological analysis of the small and large intestine of Il15 null mice did not reveal any spontaneous abnormalities when compared to WT littermates. To determine the impact of IL-15 signaling on intestinal proliferation and repair under exogenous stress, we exposed WT and Il15-/- mice to dextran sulfate sodium (DSS), a chemical irritant that disrupts the intestinal epithelial barrier and results in induction of colitis. Mice deficient in Il15 did not display a decreased susceptibility to acute DSS-induced colitis. Additionally, we found that blocking IL-15 signalling on DSS-colitis onset with the TM-[beta]1 antibody, who bind to the [beta] chain of the receptor shared by cytokines IL-2 and IL-15, prevents the overall outcome of the colitis associated inflammation in Il15ra-/- mice, but not in WT mice. Using mouse in vitro crypt enteroids from WT and Il15-deficient mice, this study demonstrates that exogenous mIL-15 promoted increased mRNA levels of the Lgr5 stem cells marker only in mutant enteroids, but not other epithelial cell linage markers tested, suggesting a role of IL-15 in intestinal cell proliferation and regeneration. Intestinal enteroids stimulated with IFN[gamma] significantly reduced in vitro basal proliferation and viability in WT and Il15-deficient enteroids. Interestingly, reduced expression of the Tnfa and Cxcl10 genes was observed in Il15-deficient small intestinal organoids under IFN[gamma] treatment. In conclusion, our results suggest that IL15Rα expression in intestinal cells may be needed for the recruitment and/or maintenance of the immune cell population responsible for tissue damage in the intestine. The reduce expression of pro-inflammatory mediators in Il15-deficient enteroids indicates that epithelial IL-15 regulates crypt homeostasis through the modulation of cytokines and chemokines, that can activate leukocytes in the intestinal epithelium to perpetuate inflammation.

Name thesis:degree_name

M. Sc.

Level thesis:degree_level

Maîtrise

Discipline thesis:degree_discipline

Biologie cellulaire

Grantor dc:publisher

Université de Sherbrooke

Year dc:date.issued

2019

Author dc:creator

• Molina Kautzman, Alicia Maria

Advisors dc:contributor.advisor

• Ramanathan, Sheela
• Asselin, Claude

• IL-15
• Intestinal epithelium
• Inflammatory bowel diseases
• Inflammation
• Ulcerative colitis
• Épithélium intestinal
• Maladie inflammatoire de l'intestin
• Colite ulcéreuse
• IL-15Rα

Language dc:language.iso

en

Handle dc:identifier.uri

http://hdl.handle.net/11143/19685

OAI identifier oai:identifier

oai:usherbrooke.scholaris.ca:11143/19685