Exogenous and Endogenous Danger Signals in Inflammatory Bowel Disease

The human chronic inflammatory bowel diseases (IBD), Crohn's disease (CD) and ulcerative colitis (UC) are ostensibly disorders of innate immunity with an exaggerated inflammatory response and loss of tolerance to the normal enteric microbial flora. In this project, we have extensively characterized innate immune responses driven by Pathogen Associated Molecular Pattern Molecules (PAMPs) and the more recently recognized Damage Associated Molecular Pattern molecules (DAMPs). The prototype DAMP, a chromatin-associated protein, high mobility group box 1 (HMGB1), is released during cellular necrosis and is secreted from activated macrophages. Extracellularly, it binds the receptor for advanced glycation end products (RAGE), as well as toll-like receptor (TLR) 2 and TLR4, important in the recognition of PAMPs. PAMPs and DAMPs trigger inflammatory signaling pathways in neighboring cells through activation of the transcription factor family, NF-kappaB.Much attention has been given to the central role played by PAMPs in the form of the enteric bacterial flora in IBD pathogenesis. We hypothesize that DAMPs also play a pivotal role in this process. Accordingly, we have determined the significance of DAMPs and PAMPs in the mucosal inflammatory response in macrophages and in vivo in mouse models of IBD.We first investigated expression of TLRs in the gut to determine cell types in the intestinal epithelium that may respond to danger signals. TLR expression was most prominent on intestinal epithelial enteroendocrine cells (EEC). Using a murine EEC line, multiple functional consequences of TLR activation were demonstrated. Second, in IL-10 deficient (-/-) mice with chronic Th1-mediated enterocolitis, we demonstrate a role for HMGB1 in macrophage activation and IBD. Lastly, we examined an in vivo therapy targeted at inhibiting the prominent downstream effector of DAMP and PAMP signaling, NF-kappaB, in murine IBD. Inhibition of activated NF-kappaB with a short cell permeable peptide inhibited chronic enterocolitis in IL-10-/- mice.In summary, this dissertation provides new insight into our understanding of intestinal innate mucosal inflammatory responses. We demonstrate the relevance of TLRs on EECs and the contribution of DAMP and PAMP signaling in disease. These results also provide proof of concept for new therapeutic approaches in IBD