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DOP006. IFI16 is dysregulated in inflammatory bowel diseases and its epithelial expression induced by pro-inflammatory cytokines

L. Pastorelli1,2, L.F. Pisani1, V. Caneparo3, M. Bawadekar3, N. Munizio2, B. Bruni4, G.E. Tontini2,5, C. Clemente4, S. Landolfo6, M. Gariglio3, M. Vecchi1,2, 1University of Milan, Department of Biomedical Sciences for Health, Milan, Italy, 2IRCCS Policlinico San Donato, Gastroenterology and Digestive Endoscopy Unit, San Donato Milanese, Italy, 3University of Piemonte Orientale, Department of Translational Medicine, Novara, Italy, 4IRCCS Policlinico San Donato, Pathology and Cytodiagnostic Unit, San Donato Milanese, Italy, 5University of Erlangen-Nuremberg, Medicine I, Erlangen, Germany, 6University of Turin, Department of Public Health and Microbiology, Turin, Italy

Background

The interferon-inducible IFI16 protein is a nuclear DNA sensor induced by several pro-inflammatory cytokines and constitutively expressed by immune and endothelial cells. It is a multifaceted protein with various functions, including regulation of transcription and innate immune response, restriction of virus replication, induction of cell apoptosis, as well as potent pro-inflammatory properties. Interestingly, the presence of anti-IFI16 autoantibodies has been shown to correlate with a milder disease course in Systemic Lupus Erythematosus; as such, IFI16 may play a role in the pathogenesis of autoimmune and inflammatory disorders. Aim of the study was to investigate IFI16 expression/localization within the inflamed intestinal mucosa from inflammatory bowel disease (IBD) patients.

Methods

IFI16 mRNA expression was assessed by means of real time RT-PCR in gut mucosal endoscopic biopsies (N = 4–7/group) from pathologic areas of Crohn's disease (CD) and ulcerative colitis (UC) patients, as well as healthy controls (CON). IFI16 expression was also evaluated by immunohistochemistry in surgically resected, full-thickness intestinal tissues collected from IBD patients and CON (N ≥ 4/group). Intestinal epithelial cell (IEC) line CaCo2 cells were cultured in the presence or absence of pro-inflammatory stimuli, such as TNF, IL-1β and IL-33, (N = 3/group) and IFI16 expression was evaluated by real ime RT-PCR, Western Blot analysis and immunostaining.

Results

UC and CD mucosa expressed higher levels of IFI16 mRNA (4.29±3.81 vs. 2.54±1.35 fold increase, respectively) than controls (set as 1). IHC for IFI16 in colonic mucosa revealed a more intense staining in IBD vs. CON. IFI16 localized to lamina propria immune cells in both IBD and CON, whereas an IEC nuclear staining was detectable only in IBD mucosa. Accordingly, when we stimulated CaCo2 cells with TNF, IL-1β or IL-33, real time RT-PCR and Western blot analysis detected high levels of IFI16 transcripts and protein, which were absent in unstimulated cells. IFI16 immunostaining showed nuclear IFI16 in stimulated CaCo2 nuclei.

Conclusion

(1) IFI16 is increased in the intestinal mucosa of IBD patients and localizes to both IEC and lamina propria leukocytes; (2) TNF, IL-1β and IL-33 induced IFI16 expression in IEC. Taken together, our study is the first to report that IEC are a primary source of IFI16 in the inflamed gut mucosa supporting its role in the IBD pathogenesis.