Claudin expression regulates mucus function - PAR-21-155 Capaldo Project Summary: Inflammatory Bowel Diseases (IBDs), encompassing both Crohn’s Disease (CD) and Ulcerative Colitis (UC), involve recurring immune activation and progressive degradation of the intestinal lining. IBDs are idiopathic diseases and current therapies frequently fail to ameliorate inflammatory symptoms, contributing to disease progression. Poor outcomes may be due to the complexities of IBD pathogenesis, which involve both genetic and environmental factors such as a high fat, low fiber western diet. Therefore, it is vital that new therapeutic strategies demonstrate efficacy in the context of genetic predisposition to IBD. This proposal aims to explore both a novel hypothesis for gene-related IBD pathogenesis, and evaluate the efficacy of a potential dietary therapy in a knockout mouse model of IBD. Importantly, loss of the cellular and/or mucus barriers of the gut is a common etiological feature of all human IBDs; including changes in mucus consistency and claudin protein expression. Our preliminary data suggest a novel functional relationship between the claudin-based barrier and the mucus barrier. Therefore, this proposal will address the following hypothesis: Inflammatory cytokines disrupt ion/fluid homeostasis in the colon through aberrant claudin expression, resulting in a weakened mucus barrier and increased susceptibility to disease. Aim 1 will directly test the hypothesis that, during inflammation, claudin proteins function to reduce mucus density and the ability of mucus to form an effective barrier. While our preliminary data strongly support this hypothesis, it is unclear if therapies can be directed at altering claudin expression. Indeed, claudin function and regulation is very poorly understood. However, high fiber/fermentable fiber diets have been demonstrated in mice to support mucophilic bacteria in the colon, thereby increasing mucus density and protective function. Will diets that support the mucus barrier prove effective in patients bearing genetic deficiencies that weaken the cellular barrier? In Aim 2 we will determine if an increase in mucus density has therapeutic benefit in a mouse model of IBD, Hepatocyte Nuclear Factor alpha (HNF4) knockout mice. HNF4 mutations are found in UC and CD, have been shown to cause changes in claudin gene expression, and removal of Hnf4a in the intestine is sufficient to cause colitis in mice. We will assess mucus function in these mice in vivo, and determine if dietary fiber will alleviate or exacerbate colitis symptoms in mice that are genetically predisposed to chronic colitis development.
