Ileal pouch transcriptomics reveal shared pathogenesis between pouchitis and ulcerative colitis

UC pouchitis is a potential model of UC. We prospectively examined the pouch transcriptomes of UC and familial adenomatous polyposis (FAP) IPAA patients to unveil molecular mechanisms of UC pouchitis susceptibility. Methods: Total RNA was isolated using the AllPrep DNA/RNA Mini Kit (QIAGEN, Cat No. 8020). RNA quality was evaluated using Bioanalyzer (Agilent, Santa Clara, CA). All RNA samples displayed RNA Integrity Number (RIN) >7. RNAseq including cDNA library preparation was processed at the Genomics Core Facility of University of Chicago (https://fgf.uchicago.edu/). Total RNA in the amount of 100-500µg per sample was depleted of ribosomal RNA using the Ribo-Zero kit (Epicentre, Madison, WI). The directional (first strand) cDNA libraries were prepared following the guide of TruSeq Stranded Total RNA Sample Preparation kit. Results: Unlike FAP patients, UC subjects exhibited a large set of differentially expressed genes (DEGs) between pouch and pre-pouch mucosa as early as 4 months after pouch functionalization. Functional pathway analysis of DEGs in UC pouch revealed: (1) Gain of colon-associated gene expressions and loss of ileum associated gene expressions, (2) enhanced state of immune/inflammatory response, and (3) suppressed xenobiotic, lipid, and bile acid metabolic pathways. These changes were corroborated upon reanalysis of a published larger cross-sectional study of UC and FAP patients. Moreover, >70% of DEGs mapped to published IBD and normal colonic microarray datasets displayed directional changes consistent with active UC, but not Crohn's disease. Conclusions: UC patients exhibit a unique transcriptomic response to ileal pouch creation that can be observed well before disease. The transcriptome alterations provide insights into pouchitis Overall design: Seventeen patients with UC and four patients with FAP were recruited at the University of Chicago and the Mayo Clinic Rochester. All patients underwent a total proctocolectomy with ileal pouch anal anastomosis (IPAA) as a standard of care. UC patients underwent a pouchoscopy for biopsy of the pre-pouch ileum and pouch at 4 months, 8 months, and 12 months after ileostomy closure. None of these patients had pouchitis.