Crosstalk between TLR5 and Notch1 signaling in epithelial cells during intestinal inflammation

During intestinal inflammation, a variety of signaling events are activated to perform several cell functions. Although the distinct roles of these pathways have been elucidated, the effects of their crosstalk activities remain to be clarified. We evaluated the crosstalk between two evolutionary conserved cell signaling systems, toll-like-receptor (TLR) 5 and Notch1, in intestinal epithelial cells during inflammation. Significant induction of the expression of Notch1 and Jagged1 was observed in the distal part of the colon, together with abundant localization of Notch1 intracellular domain (N1ICD) in the surface epithelium of inflamed colonic mucosa. By targeting intestinal epithelial cells, it was shown that recombination-signal-binding-protein-Jκ (RBP-Jκ)-mediated Notch functions are dependent on a flagellin-TLR5-mediated pathway. Conversely, using a γ-secretase inhibitor, we demonstrated that Notch synergistically increases TLR5‑mediated NF-κB activation. In addition, the effects of Notch on the NF-κB target gene interleukin-6 (IL-6) expression were revealed by evaluating the RBP-Jκ responsive element in the IL-6 promoter in vitro. Modulation of TLR5 and Notch crosstalk by transient blocking of Notch during the acute phase of colitis was beneficial for ameliorating colonic inflammation as well as disease status. In conclusion, the results suggest the effectiveness of Notch-targeted drug strategy for the treatment of intestinal inflammation.