Intestinal epithelial cells are a crucial cell type in the maintenance of the health of colonic tissue, providing a barrier between the contents of the colon, such as bacteria and foreign food antigens, and the immune system. IBD is characterized by a breakdown of the intestinal epithelial barrier leading to increased exposure of the immune system to these contents. This exposure leads to inflammation and increased breakdown of the epithelial barrier. It is now appreciated that inflammatory responses in IBD are accompanied by striking shifts in tissue metabolism, including key metabolites involved in cellular methylation. Methylation reactions are a critical component of the control of gene expression, as well as protein function. Additionally, studies have shown that changes in cellular methylation reactions play an important role in inflammatory processes and immune system modulation. These studies have revealed that epigenetic changes in DNA methylation patterns can have important consequences for these processes. Since the epithelium functions as the critical interface between the intestinal lumen and the sub-epithelial mucosa, they are thereby anatomically positioned as a central coordinator of mucosal inflammatory response and have been found to be important for control of immune system and inflammatory responses. Ongoing studies have focused on defining molecular pathways and functional targets of cellular methylation during mucosal inflammation. The initial analysis of the metabolic signature induced during inflammation in epithelial models and in colonic tissue isolated from mouse colitis models demonstrated that levels of specific metabolites associated with cellular methylation reactions are altered during epithelial inflammation in both model systems. Furthermore, expression of an enzymes central to all cellular methylation, SAM synthetase and SAH hydrolase, is increased in cells in response to inflammation. Importantly, we demonstrate that genome-wide DNA methylation is increased during hypoxia and that at least one IFN-?- regulated gene, IL-10R1, is impacted by these processes. Furthermore, we demonstrate that epithelial IL- 10R1 and IL-10 signaling play a critical role in epithelial homeostasis and inflammation resolution. These results indicate that epigenetic mechanisms play a role in the epithelial responses during inflammation. We have demonstrated that inhibition of cellular methylation exacerbates disease in mouse models of colitis indicating that these processes are protective of the epithelium. As guided by these studies, we hypothesize that IFN-?-induced epigenetic alterations modify gene expression as an integral aspect of epithelial inflammatory pathways and that alteration of DNA methylation represents a protective mechanism for the epithelium during intestinal inflammation. In this application, we will define the molecular endpoints of IFN-? regulation of cellular methylation. More importantly, we propose that these IFN-?-mediated methylation pathways could serve as templates for the development, testing and implementation as promising IBD therapies.
Ongoing experiments have revealed that cellular methylation represents an important and underappreciated modulator of the inflammatory response. This project will elucidate the mechanisms of IFN-? regulation of cellular methylation reactions and epigenetic modifications induced during inflammation in both human epithelial cell and mouse colitis models. Based on preliminary studies, we hypothesize that methylation- dependent pathways regulate the expression of genes such as IL-10R1 that are protective of the mucosal epithelium. The studies proposed here will more fully examine IFN-?-dependent mechanisms and epigenetic targets induced under conditions of ongoing inflammation.
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