Project Summary Prolonged Crohn’s disease leads to intestinal fibrosis, which is difficult to prevent or treat. The surgical resection may negatively impact a patient’s quality of life. Thus, new therapeutic approaches are actively sought after. We have recently shown that intestinal expression of antimicrobial peptide and protease inhibitor elafin is reduced in stricturing CD patients. Its potential protective effect in intestinal fibrosis has never been reported in the literature. Our preliminary data showed that elafin- overexpression inhibited preexisting colonic fibrosis in TNBS-mediated mice, Salmonella-infected mice, and SAMP1/YitFc mice. We generated an orally active elafin-Eudragit formulation for potential therapeutic applications. The elafin-Eudragit formulation reversed preexisting colonic fibrosis in TNBS-treated mice. We also discovered that elafin inhibits collagen expression in the intestinal fibroblasts by modulating several stricture-specific genes. We hypothesize that oral administration of modified elafin may be useful for treating colitis-associated intestinal fibrosis by affecting a stricture- specific pathway. We propose to (1) establish oral therapeutic regimens of modified elafin for treating intestinal fibrosis in a mouse model of preexisting intestinal fibrosis and (2) determine the cathepsin S- PAR2-miR205-ZEB1-mediated anti-fibrogenic mechanism of elafin in intestinal fibroblasts. The overall impact of this study will produce a comprehensive assessment of optimized oral elafin delivery approaches for intestinal fibrosis. This mechanistic study will reveal how and why elafin inhibits intestinal fibrosis.