Intestinal Goblet Cell-Expressed Reg4 Ameliorates Intestinal Inflammation Potentially by Restraining Pathogenic Escherichia Coli Infection

An elevated abundance of Escherichia coli (E. coli) has been linked to the onset and progression of inflammatory bowel disease (IBD). Regenerating islet-derived family member 4 (Reg4) has been isolated from patients with ulcerative colitis (UC), but its functions and involved mechanisms in intestinal inflammation are remain incompletely understood. Therefore, we generated an intestinal conditional Reg4 knockout mouse (Reg4) to address this gap by utilizing murine models of enteropathogenic E. coli (EPEC)-infected bowel and dextran sulfate sodium (DSS)-induced colitis. We here demonstrate that REG4 is increased in diseased intestinal mucosa of pediatric IBD, primarily expressed and enriched in intestinal goblet cells. Deficiency of Reg4 in the intestinal epithelium of mice leads to an increase in the Phylum Proteobacteria and in the family Enterobacteriaceae. Administration of recombinant Reg4 protein significantly mitigates EPEC-induced intestinal inflammation and injury in a murine model. In vitro, Reg4 protein suppresses the growth and motility of EPEC, subsequently reducing their adhesion and invasion to the intestinal epithelial cells. Mechanistically, the conserved mannan-binding sites (like C-lectin domain) are essential for Reg4 antimicrobial activity. Moreover, loss of Reg4 in mice increases susceptibility to DSS-induced colitis, which can be improved by gentamicin (GM), an antibiotic for Gram-negative bacteria. In conclusion, intestinal goblet cell-derived Reg4 is crucial for protection against experimental colitis, likely due to its bactericidal activity against EPEC.