It is well accepted that neuropeptides are important components of the intestinal inflammatory response. Results generated during the past funding period demonstrated for the first time that the 41 aa peptide corticotropin-releasing hormone (CRH), released locally in the gut, is a potent promflammatory mediator of acute intestinal inflammation of different etiologies. We also made the novel observation that human colonocytes bear receptors for CRH, and these receptors are upregulated during intestinal inflammation in vivo and in vitro after exposure to C. difficile toxin A or proinflamrmtory cytokines. Our overall hypothesis is that peripheral CRH and the CRN-related peptides urocortins augment acute colonic inflammation by binding to specific CRH receptors on enterocytes and macrophages. CRH and urocortin-ddpendent activation of proinflammatory transcription factors and MAP-kinase - related pathways lead to the release of proinflammatory cytokines thereby initiating of augmenting intestinal inflammation.
In aim 1 we will elucidate the participation of the NF-kappaB/kappaB system and MAP kinases in CRH receptor-mediated proinflammatory signalling in human colonic epithelial cells and macrophages. In collaboration with Dr. Ciaran Kelly we will also examine the effect of probiotics in toxin A and proinflammatory cytokines - induced increased CRH receptor expression in vitro and in vivo. Studies in aim 2 will determine the role of the CRH family of peptides (urocortin I, II, and III) in acute intestinal inflammation in mouse ileal loops in wild type and CRH receptor deficient mice and, in collaboration with Dr. Allan Walker (xenograft core), in human intestinal xenografts. In collaboration with Dr. Beth McCormick we will also assess the effect of other common GI bacteria and bacterial products (Salmonella, Shigella, LPS) on the CRH peptide family and CRH receptor expression in human colonocytes in vivo and in vitro.
Aim 3 will examine the mechanism(s) of CRH receptor regulation in intestinal epithelial cells and macrophages by proinflammatory cytokines and C. difficile toxin A. We will also study whether CRH and CRH-related peptides themselves regulate CRH receptor expression in vitro (macrophages and colonocytes) and in vivo in CRH +/+ and CRH -/- mice. Results from the proposed studies will help us dissect the mechamsm(s) by which CRH family of peptides and their receptors participate in intestinal inflammation.
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