10 - IRE1A-XBP1 CONTROLS INNATE LYMPHOID CELLS AND COLITIS-INDUCED FIBROSIS

Background: Group 2 innate lymphoid cells (ILC2s) are increased in peripheral blood and intestinal samples from IBD patients and murine colitis models. ILC2s produce a large amount of type 2 cytokines including IL-5 and IL-13 and growth factor AREG that induce goblet cell hyperplasia and mitigate acute inflammation in the gut. On the other hand, prolonged or uncontrolled ILC2 activation may contribute to chronic inflammation and tissue fibrosis. In this study, we investigated the role of IRE1a-XBP1 pathway, a regulatory hub of cellular stress response, in colitis and fibrosis in mice and patients with Crohn’s disease. 

Methods: We generated conditional knockout Ire1a^flo/floxIl5-Cre (Ire1a^ΔIl5) and Rag^-/-Ire1a^ΔIl5 mice with Ire1a deleted in ILC2s. Dextran sodium sulfate (DSS)-induced colitis and T-cell transfer colitis models were used. Human perianal ILC2s were collected for flow cytometry and ex vivo stimulations.

Results: Mouse intestinal ILC2s express high level of Ire1a (not shown). The number of ILC2s increased in colon, small intestine (SI), and esophagus of Ire1a^ΔIl5 mice with elevated proliferation marker Ki67 (Figure 1A, B). Additionally, SI and colonic Ire1a^ΔIl5 ILC2s produced more IL-5, IL-13, and AREG after ex vivo stimulation with IL-33 or IL-25 (Figure 1C). Consistently, selective IRE1 inhibitor 4u8C enhanced production of IL-13, while selective IRE1 activator IXA4 suppressed IL-13 in sort-purified human ILC2s ex vivo (Figure 1D). Bulk RNA-seq of SI Ire1a^ΔIl5 ILC2s showed reduced Rxrg and elevated fatty acid transport genes, which may explain the increased proliferation and cytokine production in Ire1a^ΔIl5 ILC2s (data not shown). Upon DSS challenge, Ire1a^ΔIl5 mice exhibited milder signs of disease including weight loss, clinical scores as well as colon shortening and histology, which was accompanied by elevations in ILC2-derived cytokines and AREG as well as heightened goblet cell differentiation and mucin production (Figure 2A). In contrast, upon adoptive T-cell transfer, Rag^-/-Ire1a^ΔIl5 mice developed worsened chronic colitis and intestinal fibrosis, which was reversed by intraperitoneal injection of neutralizing antibody against IL-13 or AREG (Figure 2B). Furthermore, CD patients with intestinal strictures expressed higher level of IL-13 in ILC2s in the blood (Figure 2C).

Conclusion: We demonstrate that IRE1a-XBP1 constrains cytokine production by intestinal ILC2s during inflammation. IRE1a deficiency in ILC2s protected against acute colitis with heightened type 2 cytokines and AREG; while loss of IRE1a exacerbated chronic colitis and fibrosis. The presence of intestinal strictures in CD patients were associated with elevated IL-13 in peripheral ILC2s. We identified IRE1a as a potential therapeutic target for patients with stricturing/fibrostenotic CD.