Selective expression of HIP/PAP gene in IBD colonic epithelial cells (EC) is associated with paneth cell metaplasia

Abstract

Background and Aims: We have established an approach to investigate IBD-associated genes using germ-free mice (Gastroenterology; 114: G43l4,1998). We demonstrated that regenerating gene (reg) I1If3and IUvwere induced in epithelial cells (EC) after bacterial reconstitution. The expression of HIPIPAP, the human homologue of reg III, was preferential in IBD EC although the number of samples was limited (Gastroenterology; 116:G34l2,1998). The aim of this study was to investigate HlPIPAP mRNA expression using a large number of samples and to characterize EC expressing this gene. Methods: HIPIPAP mRNA expression was examined by northern blotting using isolated colonic EC RNA from 17 control, 20 CD and 23 UC patients including 5 paired samples from inflamed and non-inflamed mucosae. We carried out in situ hybridization using serial tissue sections to identify the cells expressing this gene. One was routinely stained with hematoxylin eosin, and the other section with dylon, which specifically deposits to Paneth cells, to further analyze HlPIPAP expressing cells. Results: More than 60% of IBD EC (12/20 in CD, 15 /24 in UC) strongly expressed HIPIPAP mRNA but definitely none in control. When EC RNA from inflamed and non-inflamed mucosa were compared, the degree of HIPIPAP mRNA expression was predominant in cells from inflamed mucosa. In situ hybridization revealed that HIPIPAP expressing cells were completely selective and localized at the bottom of crypt in both IBD. Positive cells exhibited common features such as acidophilic granules in supranuclear space and lack of mucus, suggesting that these cells shared nature of Paneth cells. Dylon staining confirmed that HIPIPAP expressig cells were actually associated with Paneth cell metaplasia. Conclusion: HIPIPAP mRNA expression in colonic EC is strictly IBD-selective although there is no evidence that this is IBD-specific. Histochemical study clearly revealed that HIPIPAP expressing cells are associated with Paneth cell metaplasia, supporting the idea that altered gene expression in IBD EC is, at least in part, closely associated with abnormal differentiation.