Therapeutic Targeting of Endoplasmic Reticulum Stress in Inflammatory Bowel Disease

Abstract

Endoplasmic reticulum (ER) stress occurs when proteins misfold during biosynthesis in the ER. ER stress in intestinal secretory cells has been implicated in the aetiology of inflammatory bowel diseases (IBD) and intestinal inflammation in mice. Intestinal secretory cells are susceptible to ER stress due to high rates of protein synthesis, and ER stress in these cells results in reduced production of cell surface and secreted proteins leading to thinner mucus with a lower anti-microbial content, allowing penetration by luminal microbes, leading to inflammation. Cells experiencing ER stress attempt to restore homeostasis via the unfolded protein response (UPR), which enables the cells to increase the protein folding capacity of the ER. The primary focus of this thesis is to examine whether the drugs that are efficacious in IBD treatment modulate goblet cell function and ER homeostasis, and whether drugs that modulate ER stress can suppress intestinal inflammation and restore intestinal homeostasis. In order to explore the ER stress-inflammation nexus I utilized well established IBD anti-inflammatory agents, 5-Aminosalicylate (5-ASA), 6-thioguanine (6-TG), the anti-TNF antibody, infliximab, and the glucocorticoid dexamethasone (DEX). Chemical chaperones (TUDCA and sodium 4-PBA) and UPR modulators (guanabenz, salubrinal and 4μ8C) were used to investigate how modulation of ER stress affects goblet cell function and intestinal inflammation. In vivo studies were carried out in Winnie mice, which have ER stress in goblet cells due to a Muc2 misfolding mutation resulting in colitis involving both innate and adaptive immunity. To understand the direct effect of these drugs on ER stress in goblet cells in the absence of confounding inflammatory factors, in vitro experiments were performed using the human colonic adenocarcinoma LS174T cell line, a cell line containing cells with goblet cell differentiation, where ER stress was induced either by inhibition of N-glycosylation by tunicamycin or by depletion of Ca2+ by thapsigargin.