Despite major advancements in our understanding of the pathophysiology of inflammatory bowel disease, relatively little is known with respect to epigenetic factors that predispose to development of IBD. Epigenetic changes, including DNA methylation, have been implicated as risk factors for these debilitating diseases. Elevated intestinal luminal bile acids are known to exacerbate IBD symptoms, but it is not known whether changes in DNA methylation alter bile acid regulation and, thus, contribute to the severe intestinal inflammation. Luminal bile acids can become elevated either as a result of increased hepatic bile acid synthesis or decreased intestinal bile acid reabsorption. Fibroblast growth factor 19 (FGF19; FGF15 in rodents), which is induced in the ileum by reabsorbed bile acids, circulates to the liver to inhibit bile acid synthesis. Our preliminary data showed that in a dietary model of DNA hypermethylation, ileal FGF15 mRNA is repressed and the hepatic bile acid synthesis gene CYP7A1 is induced. We demonstrated that CpG methylation of the FGF15 gene is increased in this model, suggesting that methylation represses FGF15 expression. To establish the novel link between epigenetic changes and bile acid regulation, our proposed studies will test the hypothesis that DNA hypermethylation leads to dysregulation of bile acid synthesis and absorption, contributing to increased susceptibility to intestinal inflammation. The studies proposed in Specific Aim 1 will investigate the mechanisms by which DNA methylation decreases FGF15/19 expression and causes bile acid dysregulation using sophisticated in vitro and in vivo models. We will also explore the proposed link between elevated luminal bile acids and susceptibility to inflammation using established models of intestinal inflammation and transgenic mice with intestine-specific FGF15 overexpression. It is also known that intestinal bile acid absorption via the apical sodium-dependent bile acid transporter (ASBT) is rapidly modulated via phosphatases and kinases, the expression of which can be altered by DNA methylation. Thus, studies in Specific Aim 2 will investigate the effects of DNA methylation on bile acid absorption using a novel luminescence-based method for measuring bile acid uptake in live animals. Our preliminary data indicate that this method is suitable for measuring ASBT function in vitro. Our proposed studies will establish an innovative method for noninvasive, real-time measurement of bile acid absorption in animals. We will use this method to assess bile acid absorption in animal models of DNA hypermethylation. The methods established in Specific Aim 2 will provide a novel investigative tool for measuring bile acid transport in vitro and in vivo. Overall, the successful completion of the proposed studies will illuminate the mechanisms underlying how epigenetic factors such as DNA methylation contribute to bile acid dysregulation and predisposition to intestinal inflammation. This will identify novel therapeutic targets for IBD and may allow for early identification and intervention for patients with a predisposition for IBD.
Inflammatory bowel diseases (IBD) are debilitating conditions that are becoming increasingly common, although the pathogenesis of these diseases are poorly understood and treatment remains difficult. Bile acids are important molecules for maintaining intestinal health, and their dysregulation is known to worsen the symptoms of IBD and may contribute to risk of disease development. Our proposed studies will show how epigenetic modification of DNA during fetal development contributes to bile acid dysregulation and risk of IBD in adulthood. These studies will lead to an increased understanding of IBD risk factors and may lead to the development of new treatments for IBD.
