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 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.