The Role of the Tight Junction in the Serine Protease-Mediated Increase in Epithelial Barrier Function
Abstract
One of the main contributors to intestinal epithelial barrier function is the composition of the tight junction (TJ). In inflammatory bowel disease (IBD), inflammatory mediators induce disruption of the TJ and may contribute to pathogenesis. The apical addition of the serine proteases trypsin or matriptase to intestinal epithelial cell lines induces a rapid and sustained increase in transepithelial electrical resistance (TER). However, the mechanism behind this effect is incompletely understood. Determining how barrier function is modulated by serine proteases may provide further avenues to maintain barrier function and remission in IBD. It was hypothesized that serine proteases induce an increase in barrier function through modification of the TJ, and that treatment could reverse barrier disruption. Using the intestinal epithelial SCBN cell line, it was found that the response to serine proteases was independent of protease-activated receptor 2 (PAR2) and myosin regulatory light chain (MLC) phosphorylation, and mass spectrometry did not reveal a target that was being cleaved by serine proteases. Serine proteases did not enhance the recovery of barrier function after calcium depletion, and the barrier had to recover sufficiently for trypsin or matriptase to have an effect. Treatment by TNFα and IFNγ induced a concentration-dependent decrease in barrier function and prevented the increase in TER by serine proteases. Therefore, a functional tight junction is needed for the serine protease-induced increase in TER. Knockdown of occludin by siRNA prevented the increase in TER in response to serine proteases, and the membrane mobility of occludin was increased following trypsin treatment, as assessed by fluorescence recovery after photobleaching (FRAP). Thus, occludin is a key TJ protein in the serine protease mediated increase in TER. This work demonstrates that although serine proteases may not enhance barrier function in epithelia that are already disrupted, understanding the mechanisms by which they modify the junction could be used as targets for potential therapies to maintain remission.
Description
Keywords
Biology--Cell, Biology--Molecular, Physiology, Pharmacology
Citation
Ronaghan, N. (2017). The Role of the Tight Junction in the Serine Protease-Mediated Increase in Epithelial Barrier Function (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/28364