Reduced Human α-defensin 6 in Noninflamed Jejunal Tissue of Patients with Crohn’s Disease

Abstract

BackgroundMucosal barrier dysfunction is considered a critical component of Crohn’s disease (CD) pathogenesis after the identification of susceptibility genes. However, the precise mechanism underlying mucosal barrier dysfunction has not yet been elucidated. We therefore aimed to elucidate the molecular mechanism underlying the expression of human α-defensin 6 (HD6) in patients with CD.MethodsHD6 expression was induced by the transfection of an atonal homolog 1 (Atoh1) transgene and was assessed by reverse transcription polymerase chain reaction. The HD6 promoter region targeted by Atoh1 and β-catenin was determined by reporter analysis and chromatin immunoprecipitation assay. HD5/HD6/Atoh1/β-catenin expression in noninflamed jejunal samples collected by balloon endoscopy from 15 patients with CD and 9 non-inflammatory bowel disease patients were assessed by immunofluorescence.ResultsBoth promoter activity and gene expression of HD6 was significantly upregulated by the Atoh1 transgene in human colonic cancer cell line. We identified a TCF4 binding site and an E-box site, critical for the regulation of HD6 transcriptional activity by directly binding of Atoh1 in the 200-bp HD6 promoter region. The treatment with β-catenin inhibitor also decreases HD6 promoter activity and gene expression. Moreover, HD6 expression, but not HD5 expression, was found to be decreased in noninflamed jejunal regions from patients with CD. In HD6-negative crypts, nuclear accumulation of β-catenin was impaired.ConclusionsHD6 expression was found to be regulated by cooperation between Atoh1 and β-catenin within the HD6 promoter region. Downregulation of HD6 in noninflamed mucosa may contribute to mucosal barrier dysfunction of patients with CD.