Investigation of neoplastic transition of the colonic epithelium in the Winnie mouse model of spontaneous chronic colitis

Inflammatory bowel diseases (IBD) include a range of pathologies, with ulcerative colitis (UC) and Crohn’s disease (CD) representing the bulk of IBD cases. Both UC and CD are life-long immune disorders which are the cause of significant morbidity with the incidences of both diseases increasing globally. Chronic inflammation of the colon, such as that occurring in ulcerative colitis or Crohn’s colitis is associated with an increased risk of colorectal cancer. The mechanisms responsible for the transition from chronically inflamed tissue and colorectal cancer remain largely unknown. Defects in the formation of a colonic mucous lining impermeable to bacterial penetration have been associated with inflammatory bowel diseases. Genetic ablation of the predominant gel-forming mucin in the colon, mucin-2 (Muc2), produces a chronic colitis by permitting contact between the host tissues and the micro-organisms resident within the colon. Animals with defects in mucus synthesis also display an increased incidence of intestinal tumours, the development of which may accelerated by the severity of the concomitant chronic inflammation. The present study therefore aimed to investigate the utility of using the Winnie mouse to model the progression of chronic colitis to colonic cancer. Winnie carry a homozygous missense mutation in Muc2, resulting in spontaneous colitis and ER stress due to Muc2 misfolding. Since Winnie display features of UC, we intended to characterise the molecular mechanisms mediating the transition from chronically inflamed mucosa to early pre-cancerous lesions in these animals. Administration of the colonic irritant dextran sulphate sodium (DSS) in a regimen of three, seven-day cycles in Winnie mice to simulate bouts of severe inflammation was trialled. The distal colon of Winnie mice after completion of the DSS protocol revealed hyperplastic mucosa with glandular morphological abnormalities resembling pre-cancerous change. Architectural derangement consistent with high-grade dysplasia was present in 55% of Winnie receiving DSS whereas these features were absent untreated Winnie or wild-type mice (χ\(^2\) = 6.667, P i 0.01). Penetration of crypts beyond the muscularis mucosae was observed infrequently (27% of Winnie mice after DSS) but was absent in wild-type (WT) animals irrespective of treatment. Although dysplasia-like changes were evident after the completion of five DSS cycles, cessation of DSS administration allowed a return to a uniform crypt morphology. Three cycles of DSS increased expression of Ccl5, Trp53 by 10% and 28% (P <0.05) but Cav1 decreased 44% in Winnie + DSS relative to WT + DSS. Expression of Myc was unchanged in Winnie with or without DSS, but increased in WT following three cycles of DSS. Changes in distribution of vimentin and N-cadherin were not observed in the colon of Winnie suggesting that EMT was not involved in the manifestation of the observed pathology in the Winnie colon. Though the cancerous potential of the lesions observed in Winnie was unclear, the described model may be useful in exploring the progression from chronic colitis to dysplasia. Persistent alterations to Cav1 and p53 expression in particular, may be associated with an abnormal regenerative response to pro-inflammatory stimuli in the colonic mucosa.