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Inflammatory bowel disease (IBD) is the result of a chronic intestinal inflammatory response which usually occurred in colon and small intestine. Keratins constitute the intermediate filament cytoskeleton in all epithelia. The present study was intended to explore the role of Keratin 1 (KRT1) in the progress of IBD. In normal intestinal tissue, the expression of KRT1 was detected by RT-PCR and Western blot. The levels of KRT1 protein significantly decreased in serum samples of IBD patients as compared with sera of healthy controls. Immunohistochemistry revealed that the expression of KRT1 decreased in various intestinal diseases, especially in Crohn's disease and ulcerative colitis. Furthermore, down-regulated KRT1 was correlated with the severity of IBD. The overexpression of KRT1 maintained epithelial barrier in Caco-2 cells after IL-1β treatment. Furthermore, IL-1β-induced disruption of tight junction became significantly attenuated in KRT1 over-expressing Caco-2 cells as compared with control cells. Thus, KRT1 played an important role of maintaining epithelial barrier and its down-regulation in intestinal tissue was correlated with the progression of IBD. [ABSTRACT FROM AUTHOR]

The abnormal differentiation of Th17 cells aggravates ulcerative colitis (UC). Antimicrobial peptides (AMPs) exert pivotal protection functions against UC. KT2 is a cationic AMP that mediates colon cancer development. However, KT2′s function in UC remains unclear. The UC mouse model was induced by administering 2.5% dextran sulfate sodium, and the mice were given an enema of KT2. KT2′s function in UC and Th17 cell differentiation in vivo was evaluated through various molecular experiments. The KT2′s function in Th17 cell differentiation in vitro was evaluated by the proportion of CD4+ IL-17+ T cells, IL-17 levels, and RORγt expression levels. Meanwhile, the mechanism was assessed through quantitative real-time PCR, various loss-of-function assays, and dual-luciferase reporter gene assay. KT2 restrained Th17 cell differentiation in both in vivo and in vitro UC models and slowed the UC process. KT2 elevated miR-302c-5p expression, as well as restrained Th17 cell differentiation by increasing miR-302c-5p. Meanwhile, miR-302c-5p interacted with the signal transducer and activator of transcription 3 (STAT3) and negatively regulated its expression. Furthermore, our data revealed that KT2 restrained the activation of STAT3 by elevating miR-302c-5p, thereby inhibiting Th17 cell differentiation. KT2 alleviates UC by repressing Th17 cell differentiation through the miR-302c-5p/STAT3 axis. • Antimicrobial peptide KT2 can relieve the symptoms of ulcerative colitis in mice. • Antimicrobial peptide KT2 can inhibit the differentiation of Th17 cells in vitro and in vivo. • Antimicrobial peptide KT2 can up-regulate miR-302c-5p. • MiR-302c-5p targets STAT3 and negatively regulates its expression. [ABSTRACT FROM AUTHOR]