HOME
Return to Table of Contents
DELINEATION OF THE EARLY EVENTS IN THE PATHOGENESIS OF DEXTRAN SULPHATE INDUCED COLITIS
P Dharmani1, C Wong1, C De Simone2, K Chadee1
1University of Calgary, Calgary, Alberta; 2University of L’Aquila, L’Aquila, Italy
Changes in mucosal barrier function and misdirection of Th1 and Treg/Th3 immune response are the biological hallmark of intestinal inflammation in Ulcerative Colitis (UC). However, the kinetics of UC pathogenesis and the factors that primarily contribute to the initiation and perpetuation of inflammatory cascade are still not known. In the study, we determine the sequential colonic alterations that occur during the progressive development of DSS induced colitis. Colitis with ulceration and rectal bleeding was observed in healthy SD rats on 9th day of daily administration of DSS (5%w/v). Measurement of DAI showed highest score on day 9 based on rectal bleeding, stool malformation, body weight loss and ulcer indexing. Histological analysis (H&E and PAS stain) of the epithelial mucosa was done to confirm mucosal lesions and to evaluate the mucin barrier and mature mucin in goblet cells. mRNA expression analysis by Real Time quantitative PCR was done for MUC-2, MUC-3, EP2 and EP4 to determine alterations in mucosal barrier functions; for TNF-alpha and IL-1beta to evaluate alterations in inflammatory/immune responses and for TGF-beta and IL-10 to assess the immune regulatory response. A significant down regulation in the expression of mucosal barrier biomarkers MUC-3 (24 fold vs. controls) and a gradual decrease in EP receptors expression was observed from day 3 onwards. Expression of MUC-2 mRNA decreased significantly after day 3 but was present on all days. PAS staining corroborated the constant diminution of the mucus barrier and mature mucin from goblet cells from day 3 of DSS administration. A bimodal up-regulation of TNF-alpha expression on days 1 and 2 (60-70 fold vs. controls) and days 7 to 9 (35-48 fold) was the major change in the expression profile of the pro-inflammatory cytokines. Early up-regulation of TNF-alpha was a biomarker for an immediate inflammatory response against DSS while the up-regulation at later time points (day 7 onwards) probably depicted macrophage mediated cytokine secretion at the onset of colonic ulceration. Elevated expression of IL-1beta (60-80 fold increase) from days 7 to 9 implicated a dominant role for this cytokine in the later (probably macrophage mediated) stages of UC pathogenesis. Both TGF-beta and IL-10 expression showed significant down regulation from 2nd day onwards however, a resurrection was observed from day 7-9, suggestive of the activation of the natural healing mechanism. We conclude that DSS induced colitis is related to alterations in epithelial cell barrier functions that set the stage for inflammatory/immune cell activation where a Th1 cell based inflammation with TNF-alpha up-regulation and TGF-beta, IL-10 down regulation being the primary effector responses.