P146 OXPHOS INDUCTION IN HEALING: A CRITICAL MISSING STEP IN INFLAMMATORY BOWEL DISEASE?

Abstract

Abstract Background In Inflammatory Bowel Disease (IBD), mucosal healing represents a key outcome in clinical remission. Mitochondrial dysfunction is one of the major features of IBD, which is hallmarked by increased oxidative stress and impaired ATP production. However, partial wound healing continues even with repressed mitochondrial respiration in an inflammatory environment. In this study, we demonstrate that intestinal epithelial cells (IEC) responding to colitis produce a gene signature with downregulated mitochondrial expression associated with oxidative phosphorylation (OxPHOS) and upregulate epithelial-to-mesenchymal transition (EMT). These data were consistent with the notion that EMT induced in IEC is fueled by glycolysis (repressed OxPHOS). We also wish to determine if this OxPHOS repression is present in normal healing. Methods We are actively enrolling patients with Ulcerative Colitis (UC) and normal patients into a prospective study evaluating biopsy site healing. Biopsy samples from UC patients were collected in Allprotect® or PBS. Biopsy samples collected in PBS were processed for IEC isolation using enzymatic digestion followed by flow sorting of EpCAM+ cells. To investigate the healing process in colitis and normal patients, the sigmoid colon is tattooed at initial endoscopy and 10–12 biopsies are collected in Allprotect®. Patients are brought back a week later for a flexible sigmoidoscopy. The tattooed area is examined, and biopsies are obtained from the previous biopsy sites (“biopsy of the biopsy”) and collected in Allprotect®. RNA is extracted from Allprotect® preserved tissue or isolated IECs and analyzed with RT-PCR. Results Genes corresponding to subunits of NADH dehydrogenase (Ubiquinone) of complex I (ND1, ND2, ND3, ND4, ND5 and ND6) were consistently downregulated in ulcer sites of colitis patients as compared to “biopsy of the biopsy” sites near the tattoo in normal patients. As expected, samples from colitis patients exhibited significant upregulation of inflammatory markers (iNOS, NLRP3, CCL2, RANTES, TGF-b1, CCL20 and CXCL10) compared to “biopsy of the biopsy” sites in normal patients undergoing healing. Intriguingly, epithelial marker E-cadherin was noted to be decreased in samples obtained from colitis patients with concomitant increase in mesenchymal markers (Vimentin, Snail, Twist-1 and Zeb-1) compared to previously biopsied normal controls. Discussion Our data suggests that repressed OxPHOS observed in inflamed IEC from colitis patients may serves as an inducer of EMT governing delayed but partial healing in IBD. We found this to be in stark opposition to healing in normal patients, who exhibit enhanced OxPHOS associated with rapid healing. These important findings indicate OxPHOS metabolism may be an important target for therapeutic agents to improve healing in refractory colitis.