IRE1α-XBP1 CONTROLS GROUP 3 INNATE LYMPHOID CELLS IN INFLAMMATORY BOWEL DISEASE

Abstract BACKGROUNDS Group 3 innate lymphoid cells (ILC3s) recently emerged as important regulators and potential drug targets for IBD. However, the response of ILC3s to environmental stimuli during intestinal inflammation remains elusive. IRE1α-XBP1 is the most conserved pathway of the endoplasmic reticulum stress response that plays an important role in intestinal homeostasis. IRE1α mediates the alternative splicing of Xbp1 mRNA to produce a potent transcription factor XBP1s. Our preliminary data suggested that IRE1-XBP1 is induced during the activation of intestinal ILC3s. METHODS We generated conditional knockout Ire1αflox/flox,Rorc-Cre (Ire1αΔRorc) mice with Ire1α deleted in ILC3s. Intestinal infections were induced by Citrobacter rodentium and Clostridium difficile. In the acute phase of C. rodentium and C. difficile infection, IL-22 secreted by ILC3s, but not adaptive immune cells, is crucial for the host defense. Dextran sodium sulfate (DSS) was given in drinking water to induce colitis. We recruited patients with active Crohn’s disease (CD) and collected ileal biopsies during routine colonoscopy before starting a new biologic therapy. Mucosal immune cells were isolated from tissue samples for analysis of ILC3s by flow cytometry. RESULTS In murine intestinal ILC3s, the activity of IRE1α-XBP1 follows a robust 24h circadian rhythm which parallels that of clock genes and cytokines including IL-22 and IL-17A. IRE1α-XBP1 in intestinal ILC3s is further activated in response to inflammation/infection in mice and in patients with IBD compared to healthy controls. The IRE1α-XBP1 activation in stimulated ILC3s requires mitochondrial reactive oxygen species. Using the Ire1αΔRorc mice, we demonstrate that IRE1α-XBP1 is critical for cytokine expression by ILC3s. XBP1s binds to the promoters of Il-22 and Il-17a in activated ILC3s. Ire1αΔRorc mice loss the rhythmic expression of Il-22 and Il-17a by ILC3s in the gut. Additionally, Ire1αΔRorc mice are highly vulnerable to C. rodentium and C. difficile infection as well as DSS-induced colitis (Figure 1). The Ire1αΔRorc mice exhibit reduced IL-22 and IL-17A in ILC3s and impaired epithelial barrier function with diminished expression of mucins and antimicrobial peptides. The susceptibilities of Ire1αΔRorc mice to infections and colitis are rescued by injection of recombinant IL-22. Importantly, the frequency of ILC3s expressing XBP1s in ileal mucosa from CD patients positively correlates with response to therapies (Figure 2). CONCLUSIONS IRE1α-XBP1 controls ILC3s by activating IL-22 and IL-17A that are crucial for intestinal barrier function. Loss of IRE1α-XBP1 in ILC3s impairs the optimal and rhythmic expression of protective cytokines and renders the mice more susceptible to intestinal infections and colitis. Moreover, XBP1s in mucosal ILC3s may become a useful marker to predict response to therapies in CD patients.