Enteroendocrine Cells Regulate Intestinal Barrier Permeability.

The intestinal epithelial barrier is essential for nutrient absorption and protection against ingested pathogens and foreign substances. Barrier integrity is maintained by tight junctions which are sensitive to inflammatory signals, thus creating a feed-forward loop with an increasingly permeable barrier that further drives inflammation and is the hallmark of inflammatory bowel disease. There are currently no therapeutic strategies to improve the intestinal epithelial barrier. We hypothesized that enteroendocrine cells may play an unappreciated role in maintaining barrier integrity. To test this hypothesis, we seeded human intestinal enteroids with genetic loss of enteroendocrine cells on Transwell filters and evaluated transepithelial electrical resistance, paracellular permeability, and the localization and abundance of junctional proteins. We found that enteroendocrine cells were required to maintain a healthy barrier in crypt-like "stem" and villus-like differentiated cultures. Additionally, exogenous supplementation of enteroendocrine-deficient cultures with the hormones peptide tyrosine tyrosine (PYY) and the somatostatin analog octreotide was sufficient to rescue many aspects of this barrier defect both at baseline and in the presence of the inflammatory cytokine tumor necrosis factor (TNF). Surprisingly, these improvements in barrier function occurred largely independently of changes in protein abundance of junctional proteins zona-occludens 1, occludin, and claudin-2. These findings support a novel role for enteroendocrine cells in augmenting epithelial barrier function in the presence of inflammatory stimuli and present an opportunity for developing therapies to improve the intestinal barrier.