In vivo analysis of intestinal epithelial barrier maintenance, regulation, and repair

Epithelial surfaces function to define the boundary between various tissue compartments. The intestinal epithelium is unique because it must provide a barrier between the harsh environment of the lumen of the intestine and the rest of the body, but must also maintain selective permeability to allow for nutrient and water transport across the mucosa. A functional epithelial barrier is critical to intestinal homeostasis. The tight junction seals the space between epithelial cells and is the main determinant of paracellular permeability. Numerous intestinal disorders are characterized by increased paracellular permeability, or barrier dysfunction.I therefore developed live animal imaging techniques to examine tight junction morphology and determine the mechanisms by which epithelial barrier function is maintained or restored in three increasingly severe models of barrier loss in vivo: (1) cytokine-induced barrier dysfunction, (2) cytokine-induced single cell shedding, and (3) epithelial wound closure. These are the first images of tight junction protein trafficking and remodeling in vivo in real time (Supplementary files videos 1-4).I have discovered important roles for caveolar endocytosis, vesicular trafficking, and cytoskeletal regulation. The mechanistic understanding of the process occurring in live animals is an advancement over previous in vitro and ex vivo studies. These studies have furthered understanding of tight junction regulation and barrier maintenance during physiological and pathophysiological events that could previously only be investigated using in vitro and ex vivo systems.