Neuropeptides are major participants in the pathogenesis of colonic inflammation and Inflammatory Bowel Disease (IBD). We showed that the neuropeptide substance P (SP) plays a dual role in colitis, acting as a proinflammatory mediator in the acute phase of colitis, but promoting mucosal healing during the repair phase of inflammation. Recent novel results from our laboratory substantially advanced our understanding on the multiple roles SP-NK-1R interactions play in the pathophysiology of IBD-related colitis. We show that SP interaction with its neurokinin-1 receptor (NK-1R) mediates angiogenesis in vivo and in vitro by inducing secretion of the pro-angiogenic factor CCN1 and likely VEGF from colonocytes, which in turn stimulates neo- angiogenesis in human intestinal microvascular endothelial cells. This is the first paradigm of a neuropeptide involved in angiogenesis-IBD-related inflammation. We also found increased NK-1R expression and neoangiogenesis in the mesenteric fat depots during experimental colitis and identified expression of NK-1R in human mesenteric preadipocytes that respond to SP by increased activation of NF-B-related proinflammatory genes. These findings link for the first time SP-NK-1R-dependent changes in mesenteric fat depots with colitis and may be pathophysiologically relevant since abdominal fat wrapping and fat expansion are common findings in IBD patients. Our hypothesis is that SP via NK-1R stimulates expression of pro-angiogenic molecules on colonocytes and human mesenteric preadipocytes, which then promote angiogenesis related to the pathophysiology of colitis.
Aim 1 will study the role of SP in angiogenesis in the colonic mucosa during colitis using in vivo and in vitro angiogenesis-related systems. Studies in aim 2 will identify the signaling pathways in SP-mediated transcription of angiogenic factors in human colonocytes and mouse colon during colitis, focusing initially in CCN1 and VEGF. We also hypothesize that SP-mediated responses in human preadipocytes influence colitis in two ways, first by enhancing development and progress of colitis and second by stimulating proliferation of preadipocytes, leading to fat expansion and fat expansion-associated angiogenesis. Thus, aim 3 will study the effect of SP on mesenteric fat depot expansion during colitis, and investigate the role of angiogenesis in this response. Experiments investigating whether SP regulates fat expansion in human preadipocytes and changes the activity of related signaling molecules in these cells are also included in this aim. Our results might provide important insights on the importance of SP and NK-1R in angiogenesis during colitis and their role in inflammation of mesenteric fat depots observed in IBD and animal models of experimental colitis.
This project will examine the mechanisms by which the neuropeptide substance P stimulates angiogenesis during intestinal inflammation in the colon and the mesenteric fat depots and how these responses participate in the pathogenesis of intestinal inflammation and Inflammatory Bowel Disease. Part of this project will also examine whether SP-mediated responses in human preadipocytes influence pathways that link colitis with the metabolic syndrome and insulin resistance.
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