Published online Oct 7, 2016. doi: 10.3748/wjg.v22.i37.8334
Peer-review started: June 28, 2016
First decision: July 29, 2016
Revised: August 15, 2016
Accepted: September 6, 2016
Article in press: September 6, 2016
Published online: October 7, 2016
To determine if exacerbation of pre-existing chronic colitis in Winnie (Muc2 mutant) mice induces colonic dysplasia.
Winnie mice and C57BL6 as a genotype control, were administered 1% w/v dextran sulphate sodium (DSS) orally, followed by drinking water alone in week-long cycles for a total of three cycles. After the third cycle, mice were killed and colonic tissue collected for histological and immunohistochemical evaluation. Inflammation and severity of dysplasia in the colonic mucosa were assessed in H&E sections of the colon. Epithelial cell proliferation was assessed using Ki67 and aberrant β-catenin signalling assessed with enzyme-based immunohistochemistry. Extracted RNA from colonic segments was used for the analysis of gene expression using real-time quantitative PCR. Finally, the distribution of Cxcl5 was visualised using immunohistochemistry.
Compared to controls, Winnie mice exposed to three cycles of DSS displayed inflammation mostly confined to the distal-mid colon with extensive mucosal hyperplasia and regenerative atypia resembling epithelial dysplasia. Dysplasia-like changes were observed in 100% of Winnie mice exposed to DSS, with 55% of these animals displaying changes similar to high-grade dysplasia, whereas high-grade changes were absent in wild-type mice. Occasional penetration of the muscularis mucosae by atypical crypts was observed in 27% of Winnie mice after DSS. Atypical crypts however displayed no evidence of oncogenic nuclear β-catenin accumulation, regardless of histological severity. Expression of Cav1, Trp53 was differentially regulated in the distal colon of Winnie relative to wild-type mice. Expression of Myc and Ccl5 was increased by DSS treatment in Winnie only. Furthermore, increased Ccl5 expression correlated with increased complexity in abnormal crypts. While no overall difference in Cxcl5 mucosal expression was observed between treatment groups, epithelial Cxcl5 protein appeared to be diminished in the atypical epithelium.
Alterations to the expression of Cav1, Ccl5, Myc and Trp53 in the chronically inflamed Winnie colon may influence the transition to dysplasia.
Core tip: Patients with ulcerative colitis (UC) are at increased risk of developing colonic cancer. Understanding progression to early dysplastic change in the UC-associated inflammation in the colon required a suitable animal model. Winnie mice develop a UC-like chronic colitis and endoplasmic reticulum stress due to a Muc2 mutation encoding a misfolded mucin-2. We hypothesised that exacerbation of pre-existing chronic inflammation using colitogenic dextran sulphate sodium in a model of spontaneous colitis would induce colorectal tumourigenesis. This study demonstrated that exacerbation of colitis resulted in epithelial hyperplasia in the distal colon and crypt abnormalities resembling dysplasia. Altered expression of genes known to modify tumour growth, specifically Cav1, Ccl5, Myc and Trp53, in Muc2 mutants may predispose to early neoplastic change in the inflamed colon.