Salmonella biases epithelial differentiation through Wnt and Notch signaling, which may contribute to diarrheal pathogenesis
Non-typhoidal Salmonella is one of the most burdensome foodborne diarrheal pathogens. Previous work has shown a decrease in expression of the chloride/bicarbonate exchanger SLC26A3 (Down-Regulated in Adenoma; DRA) following Salmonella infection and it is thought that diarrheal symptoms could stem from the downregulation of DRA. However, despite its prevalence, the mechanism by which Salmonella elicits diarrhea is not entirely known. To elucidate this, we have developed an enteroid model to recapitulate both the absorptive and secretory lineages of the intestinal epithelium. Enteroid-derived monolayers (EDMs) were infected with Salmonella where relevant protein expression was studied using qRT-PCR and western blot. Infection reduced expression of DRA and Hes1 while upregulating ATOH1 and Muc2. Hes1 is a Notch pathway downstream signaling molecule and thus a precursor to the absorptive epithelial lineage that expresses DRA. ATOH1, in contrast, is a Wnt pathway downstream signaling molecule and a precursor to secretory lineages, including goblet cells that express Muc2. The involvement of Notch was further investigated by inhibiting Notch signaling using a γ-secretase inhibitor, which reproduced the downregulation in Hes1 and DRA and upregulation in ATOH1 and Muc2 seen with infection. Secretory transporters NKCC1 and CLCA1 were also upregulated following infection, which might contribute to the imbalance between absorption and secretion. Our findings suggest that the pathogenesis of diarrheal disease in the setting of Salmonella infection may reflect Notch inhibition and an accompanying shift in differentiation from absorptive to secretory cell types and transporters, a decreased capacity for absorption, and thus the accumulation of diarrheal fluid.