Several pieces of evidence indicate that substance P (SP) via binding to high affinity neurokinin-1 receptor (NK-1R) plays a critical role in the modulation of inflammatory responses in many organs, including the GI tract. Thus, both SP and NK-1R receptor expression is increased in the small intestine and colon of animal models of intestinal inflammation and in the colonic mucosa of patients with inflammatory bowel disease (IBD), and Clostridium difficile associated colitis. We showed that NK-1R are localized in colonic epithelial cells and lamina propria macrophages and that binding of SP to these receptors activates the nuclear factor kappaB (NF-kappaB) leading to the release of proinflammatory cytokines. NK-1R communicates with the epidermal growth factor receptor (EGFR) and such communication plays an important role in the development of prolonged colitis. Moreover, IL-1beta, and TNF-alpha, two cytokines linked to colonic inflammation, can upregulate the NK-1R by a mechanism involving the NF-kappaB/IkappaB system. However, the signaling pathways involved in SP-induced NF-kappaB activation and increased expression of proinflammatory genes is not known. As well, very little is known on the molecular events leading to increased NK-1R expression during colonic. The central hypothesis in this proposal is that the NF-kappaB/lkappaB system is critical in both, SP-induced upregulation of proinflammatory genes, as well as in upregulation of its receptor. An additional hypothesis is that SP-mediated NK-1R-EGFR trans activation is linked to proinflammatory signaling pathways, important for the development of acute colitis.
Aim 1 will elucidate the participation of the NF-kappaB/IkappaB system in substance P-neurokinin- 1 receptor-induced proinflammatory signaling in colonic epithelial cells by determining the specific kinases and Ird3 isoforms targeted following SP receptor binding.
Aim 2 will examine the role of MAP kinases and MAP kinase-related pathways in SP-NK-1R - induced NFrd3 activation in proinflammatory gene expression in colonic epithelial cells. Involvement of Ras and EGFR activation will also be determined.
Aim 3 will define the molecular mechanisms regulating neurokinin-1 receptor gene expression in THP-1 cells and examine the importance of these mechanisms in lamina propria macrophages. Our results will provide important insights on the mechanisms of SP-NK-1R mediated proinflammatory signaling in inflammatory responses, including human colitis.
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