Negative Regulation of Inflammation: Implications for Inflammatory Bowel Disease and Colitis Associated Cancer

The ability to sense and respond to external environmental signals is closely regulated by a plurality of cell signaling pathways, thereby maintaining homeostasis. In particular, the inflammatory signaling cascade contributes to cellular homeostasis and regulates responses prompted by external stimuli. Such responses are diverse and range from a variety of processes, including tissue repair, cell fate decisions, and even immune-cell signaling. As with any signaling cascade, strict regulation is required for proper functioning, as abnormalities within the pathway are often associated with pathologic outcomes. A hyperactive inflammatory response within the gastrointestinal tract, for example, contributes to inflammatory bowel disease (IBD), presenting as Crohn’s disease or ulcerative colitis. Furthermore, as a chronic condition, IBD is associated with an increased risk for the development of colitis-associated cancer.

In order to resolve inflammation and thus restore homeostasis, negative regulation may be utilized to mediate the activity of inflammatory molecules. The mechanistic action of a specific negative regulator of interest, interleukin receptor associated kinase M (IRAK- M), is explored in detail within the present dissertation. Investigation of IRAK-M in mouse models of colitis, which mimics human IBD, and in mouse models of inflammation-driven tumorigenesis, which models colitis associated cancer, demonstrated that loss of this molecule contributes to host protection. Therefore, IRAK- M may be a suitable target for inhibition in order to advance therapeutic options for human patients afflicted with a GI-related inflammatory disease, such as IBD and colitis associated cancer.

Furthermore, an ex vivo method that models the interaction of intestinal epithelial cells with microbes present in the GI tract was optimized and is described in the present dissertation. This method takes advantage of primary intestinal derived organoids, also termed “mini-guts”, which display similar features corresponding to intestinal tissue in vivo. For this reason, the use of “mini-guts” has several advantages, particularly for the enhancement of personalized medicine. The method discussed herein aims to normalize experimental conditions in order to enhance reproducibility, which can further be used to uncover microbial-epithelial interactions that contribute to a pathological state, such as IBD. Finally, this method of intestinal epithelial cell culture was utilized to evaluate the role of a protein, termed NF-κB inducing kinase (NIK), in intestinal epithelial cell growth and proliferation. Ultimately, ex vivo organoid culture can serve as an important model system to study the contribution of NIK in intestinal stem cell renewal, cancer progression, as well as in maintenance of the integrity of the gastrointestinal barrier.