Epithelial Notch-1 Drives the Mucosal Immune Response in the Gut

Introduction: The Notch-1 signaling pathway is responsible for homeostatic tight junction (TJ) expression in vitro and maintenance of barrier function. Lamina propria lymphocytes (LPLs) promote barrier function in vivo in the RAG1-adoptive transfer model of colitis, putatively due to the Notch-1 pathway. Notch-1 activation is increased in Crohn's disease epithelia compared to normal or ulcerative colitis. We sought to determine the role of epithelial Notch-1 in the lympho-epithelial crosstalk in health and disease. Methods: Wild type (WT) mice were treated with Notch-1 or scrambled siRNA with or without a 3 % DSS regimen. We studied the impact of in vivo Notch-1 knock-down (KD) on epithelial differentiation, barrier function and mucosal immune response. Human PBMCs were stimulated with supernatants from the Notch-1 KD Caco-2 cells in order to assess the immuno-modulatory role of epithelial Notch-1 in vitro. Results: Notch-1 and claudin-5 expression was decreased in Notch-1 siRNA treated animals, and permeability was increased. These mice were more susceptible to DSS colitis and showed decreased LP and MLN FoxP3+ cells, decreased colonic chemokine mRNA expression and effector T cell cytokine secretion. Notch-1 KD Caco-2 cells had lower basal cytokine expression and dampened response to TNF[alpha]. The supernatant from these cells induced lower levels of FoxP3 expression in CD4+ T cells as well as IL-6, -10 and IFN[gamma] secretion from stimulated PBMCs. Conclusion: We identified that epithelial Notch-1 is required for appropriate activation of intestinal epithelial cells at steady state and during inflammation. Epithelial activation under the control of Notch-1 expression modulates chemokine and cytokine secretion, and FoxP3 and effector T cell responses. We showed that epithelial Notch-1 controls the immune function of the epithelium, which, in turn, elicits T cell responses. Our findings highlight an indispensable role for Notch-1 mediated signaling in the intricate epithelial-immune crosstalk, and validate that epithelial Notch-1 is necessary and sufficient to support protective epithelial pro-inflammatory responses. Intestinal epithelial Notch-1 signaling shapes the underlying immune response at steady state and during inflammation. Overall, epithelial Notch-1 bridges innate and adaptive immunity in the gut.