Mechanism of Interleukin-1β Induced-Increase in Mouse Intestinal Permeability In Vivo

Interleukin-1 beta (IL-1 beta) has been shown to play an essential role in mediating intestinal inflammation of Crohn's disease and other inflammatory conditions of the gut. Previous studies from our laboratory have shown that IL-1 beta causes an increase in intestinal tight-junction permeability in Caco-2 monolayers in vitro. However, the IL-1 beta effect on the intestinal epithelial barrier in vivo remains unclear. Aims: the major aims of this study were to examine the effect of IL-1 beta on mouse intestinal epithelial barrier in vivo and to delineate the mechanisms involved using an in vivo model system consisting of a recycling perfusion of mouse small intestine. Intraperitonial injection of IL-1 beta at varying doses (0-10 mu g) caused a concentration-dependent increase in mouse intestinal permeability to the paracellular marker dextran (10 KD), and the maximal increase in dextran flux occurred at IL-1 beta dose of 5 mg. IL-1 beta treatment caused an increase in myosin light-chain kinase (MLCK) mRNA and protein expression in the small intestinal tissue starting at 24 h, which continued up to 72 h. Additionally, IL-1 beta did not cause an increase in intestinal permeability in MLCK-deficient mice (C57BL/6 MLCK-/-). MLCK inhibitor ML-7 (2 mg/kg body weight) also inhibited the IL-1 beta-induced increase in small intestinal permeability. The IL-1 beta-induced increase in mouse intestinal permeability was associated with an increase in NF-kappa B activation. The intestinal tissue-specific silencing of NF-kappa B p65 inhibited the IL-1 beta-induced increase in intestinal permeability and increase in MLCK expression. These data show for the first time that IL-1 beta causes an increase in mouse intestinal permeability in vivo. These data suggested that the mechanism of IL-1 beta-induced increase in mouse intestinal permeability in vivo involved NF-kappa B p65-induced activation of the mouse enterocyte MLCK gene.