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Manipulating Goblet Cell Function to Protect Against Enteric Infection
Mucus production by goblet cells serves as one of the crucial mucosal defenses at the interface between the eukaryotic and prokaryotic cells and yet the immunoregulatory pathways involved remain uncharacterized. The inner mucus layer of the intestine functions as a barrier, which serves to minimize microbial translocation, prevents excessive immune activation, and decrease infection. Here we have described methodology to alter the thickness of the inner mucus layer through treatment with antibiotic or a phytochemical. We showed that the antibiotic metronidazole caused a significant thinning of the inner mucus layer accompanied by a dramatic change in the microbial community structure. In contrast, treatment with the phytochemical eugenol resulted in a significant thickening of the inner mucus layer that was accompanied by a change in the microbial community. These changes in community structure were complimentary; sequencing showed that groups depleted by metronidazole treatment were more abundant with eugenol treatment. To investigate how changes in the integrity of the inner mucus layer affect intestinal defense, Citrobacter rodentium (Cr) was used to examine susceptibility to enteric-induced colitis. Metronidazole-induced reduction in mucus thickness correlated with exacerbated severity of Cr-induced colitis. Thickening of the inner mucus layer with eugenol treatment resulted in protection from Cr-induced colitis. Further, we identified a novel innate immune pathway involved in regulation of goblet cell function and mucus layer production. The NLRP6 inflammasome was shown to regulate mucus secretion and deficiency in any component of the NLRP6 inflammasome resulted in impaired goblet cell function preventing mucin granule exocytosis and mucus layer formation. Abrogated mucus secretion led to increased invasiveness and pathology of Cr infection. Mechanistically, NLRP6 deficiency led to stalled autophagy in goblet cells, providing a link between inflammasome activity, autophagy, mucus exocytosis, and antimicrobial barrier function.
Keywords: mucus, goblet cell, Citrobacter rodentium, phytochemical, eugenol