REGULATION OF COLONIC MACROPHAGES AND TYPE-17 AND REGULATORY T CELLS IN DSS-COLITIS BY IBD-ASSOCIATED TRANSCRIPTION FACTOR, CREM.

BACKGROUND: Recent genome wide association studies (GWAS) performed by our laboratory identified polymorphisms at the locus containing the gene, cAMP-responsive element modulator (CREM), that influence Entamoeba histolytica (+) diarrheal disease susceptibility in children. CREM is a cAMP-responsive transcription factor that regulates genetic expression and epigenetic modulation in a context- and cell-specific manner. Polymorphisms at this locus have been previously associated with IBD susceptibility, suggesting CREM regulates enteric inflammation in infectious and autoimmune colitis. METHODS: Mice were generated with either a tamoxifen-inducible global deletion or an intestinal epithelial cell (IEC)-specific deletion of Crem. Dextran-sodium sulfate (DSS) was administered to chemically induce colitis and mice were assayed for weight loss, clinical score, spectral flow cytometry of colonic lamina propria and mesenteric lymph node white blood cells, and shallow shotgun whole genome sequencing of fecal samples. RESULTS: Tamoxifen-inducible global deletion of Crem significantly ameliorated DSS-colitis severity as measured by clinical scoring and weight loss over the course of disease (p = 2.29 × 10(-15), p = 2.24 × 10(-21), respectively). Protection was not phenocopied when Crem was deleted exclusively in IECs. When sampled during acute colitis, protection seen in Crem-deleted mice was associated with a significant increase in macrophages, and RORγt(+) regulatory (pTregs) and T helper (Th17) cells in the colonic lamina propria, along with an increase of T-follicular like helper cells in the mesenteric lymph node. CONCLUSIONS: Inducible global deletion of Crem reduced the severity of DSS colitis while increasing colonic macrophages, RORγt(+) regulatory (pTregs) and T helper (Th17) cells. Future work will investigate the aforementioned cell types to determine the mechanism by which CREM aggravates DSS-colitis, thereby defining the immunoregulatory role of CREM in intestinal inflammation with the goal of identifying new therapeutic targets for IBD.