Abstract
INTRODUCTION: The prevalence of inflammatory bowel disease (IBD) is increasing globally whilst genetic factors account for only a small portion of overall disease variance. Accumulating evidence has highlighted the importance of epigenetic regulation in IBD pathogenesis. We aimed to identify key epigenetic modulators of IBD in a population of increasing disease incidence and characterize the mechanisms involved. METHODS: Customized PCR array containing 128 well-defined epigenetic modulators were performed and candidate genes were validated in 96 tissues from patients with Crohn's disease (CD), ulcerative colitis (UC) andmatched healthy controls using quantitative RT-PCR,Western blot and immunohistochemistry. Functional assays were performed using normal colonic epithelium cell line, NCM460, in which histone modification status and expressions of inflammatory cytokines were monitored upon small-molecule inhibition or RNA interference. RESULTS: Seven epigenetic modulators were differentially expressed in inflamed IBD tissues compared with controls. Amongst them, lysine acetyltransferase 2B (KAT2B) mRNA and protein levels were significantly down regulated in CD and UC inflamed tissues in a validation cohort (p< 0.05). KAT2B proteins were localized abundantly in nuclei of epithelial cells of non-inflamed colonic tissues but not in paired inflamed tissues. Inhibition of KAT2B by anacardic acid (AA), a specific small-molecule KAT2B antagonist, or small-interfering RNA (siRNA) in NCM460 cells reduced acetylation level of histone H4, but not histone H3 lysine 9 and lysine 14. Moreover, siRNA knockdown of KAT2B significantly decreased IL-10 but increased IL-1β and IL-18 expression in NCM460 cells, these changes were dose-dependent and influenced by AA treatment. CONCLUSION: Our findings demonstrated for the first time a novel epigenetic link between histone modification and IBD through KAT2B. Downregulation of KAT2B may promote histone deacetylation that leads to suppression of IL-10, a key anti-inflammatory cytokine critical for innate and adaptive inflammatory responses. Ongoing functional characterization of tissue or disease-specific epigenetic variations in IBD will provide insight into biological pathways that may translate into new therapeutic approaches.
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