Inflammation plays an integral role in human physiology;acute inflammation serves a vital purpose to clear infections from the body. By contrast, chronic inflammation has been implicated in disorders such as rheumatoid arthritis and inflammatory bowel disease (IBD). The etiology of IBD is complex and the current consensus implicates a combination of host susceptibility, environmental factors and an aberrant response to gut microbiota. A central driver of the inflammatory response is tumor necrosis factor (TNF), a pro-inflammatory cytokine. Overproduction of TNF has been observed in IBD and treatment with anti-TNF antibodies reduces symptoms, yet the spatiotemporal dynamics of Tnf upregulation are still poorly understood. One factor that has been suggested to underlie changes in inflammatory signaling and disease development is epigenetics, though specific factors that contribute to epigenetic regulation of Tnf expression in IBD remain to be elucidated. One strategy to overcome this road block is to use a model system in which strong genetics and whole organism live-imaging can be exploited. Zebrafish has proven a powerful system in modeling human disease states and an optically transparent body and digestive physiology similar to mammals make it amenable to study IBD onset. Our lab has recently performed a forward genetic screen for zebrafish with intestinal defects and recovered aa51.3, an IBD-like mutant with epithelial cell shedding and excess apoptosis, loss of epithelial folds and decreased barrier function in the intestine. When crossed to an inflammation-responsive tnfa transgenic reporter line generated for this study, aa51.3 mutants displayed elevated tnfa along the entire length of the intestine. Exome sequencing followed by positional cloning identified a causative splice-site mutation in the gene encoding Ubiquitin-like containing PHD Ring Finger 1 (Uhrf1), which plays a fundamental role in epigenetic regulation of gene expression by promoting DNA maintenance methylation. The long-term objective of this research is to define how loss of maintenance methylation causes IBD-like defects in the intestinal epithelium. This research will provide insights into how changes in methylation may promote the development of inflammatory diseases and may uncover new therapeutic targets. To achieve this objective, the following specific aims are proposed: 1) Dissect the role of tnfa expression in the loss of epithelial integrity in uhrf1 mutants and 2) Investigate if tnfa upregulation occurs in cells that have lost CpG DNA methylation. This work is in full alignment with the mission of the NIH as it addresses a significant gap in understanding of inflammation and IBD susceptibility and may uncover new therapeutic targets.
Inflammatory bowel disease (IBD) affects over one million Americans yet diagnosis of the disease is hindered by lack of understanding of the early phases of disease onset and susceptibility. The research proposed here aims to characterize how loss of maintenance methylation leads to elevated tumor necrosis factor expression and decreased barrier function in a new zebrafish IBD-like mutant. This research may lead to new therapeutic avenues for the treatment of IBD and is in alignment with the NIH's mission to improve human health.