P0567 THE HEDGEHOG TRANSCRIPTION FACTOR GLI3 MEDIATES THE DEVELOPMENT OF INTESTINAL METAPLASIA

Abstract

Introduction: Helicobacter pylori infects approximately 50% of children worldwide. Chronic infection can initiate a cascade of pathologic changes within the stomach initially with chronic gastritis and atrophy to intestinal metaplasia (IM). Subsequently, in many cases of IM, carcinoma ensues. The pathobiology of IM, however, is not well understood. Recently, Hedgehog signaling molecules have been identified in both human digestive tract tumours as well as in cell lines derived from digestive tract carcinoma. In the embryo Sonic hedgehog (Shh) contributes to the proper specification of the glandular stomach. In its absence, intestinal transformation of the stomach occurs. The aim of this study was to determine the role of the Hedgehog signaling pathway in the development of IM. Methods: We examined mice mutant in Sonic hedgehog, and the downstream transcription factors, Gli2 and Gli3. All three homozygous mutant mice die at or just before birth. Therefore, pregnant mice from wildtype and heterozygous crosses of the three mutant strains were sacrificed at embryonic day 18.5 and their stomachs were dissected out, fixed in paraformaldehyde, dehydrated and embedded in paraffin. Sections were cut and examined for alkaline phosphatase staining (AP). Immunostaining was performed for the intestinal transcription factor, Cdx2, and intestinal mucin, Muc2, two known markers for IM. Results: The stomachs of both Shh and Gli3 but not Gli2 mutant mice demonstrated positive staining for AP in the distal hindstomach. In the Gli3 but not Shh mutant stomachs, both Cdx2 and Muc2 were found expressed in the distal hindstomach. Gli2 mutant stomachs were also negative for Cdx2 and Muc2 expression. Conclusion: The absence of the activated transcription factor Gli3 leads to the development of intestinal metaplasia in the glandular stomach of the mouse. Concurrently, the transcription factor Cdx2 along with Muc2, which Cdx2 is known to regulate, are actively expressed. However, the presence of the cleaved form of Gli3, as in Shh mutant stomach, prevents this activation. We conclude, therefore, that both forms of Gli3 participate in defining the identity of the gastric gland. Further study of the Hedgehog signalling pathway is likely to improve our understanding of the pathogenesis of intestinal metaplasia.