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No description available.

Inflammatory bowel disease (IBD) confers a high risk of development of colitis-associated colorectal cancer in patients with extensive colitis. Crypt fission is a mechanism of clonal expansion in the intestinal epithelium. Although fission is rare in the normal colon, many crypts in IBD patients are in the process of fission. Protumourigenic mutations can spread through the entire inflamed colon relatively quickly indicating that stem cell dynamics are altered in IBD. Some patients with IBD develop pseudopolyps as a result of mucosal ulceration and epithelial regeneration. The aim of this PhD was to investigate the effect of inflammation on niche succession, the crypt cycle and the expansion of clones in the IBD intestine. Pseudopolyps were examined as potential sites for clonal expansion by determining the frequency of mutated pseudopolyps and proliferative potential, and examining their microRNA (miRNA) profile relative to inactive, active and dysplastic mucosa, and adenoma and cancerous tissue. This thesis will show that crypt fission cycles in inflammatory bowel diseased colon are protracted and that each stage of crypt fission appears to be slow. Overall, clonally related adjacent IBD crypts seem to share a more recent common ancestor than non-related IBD crypts, supporting increased crypt fission rates in IBD. The proliferative drive induced by continuous inflammation and mucosal repair in ulcerative colitis (UC) appears to promote the expansion of CCO-deficient patches. Furthermore, niche succession appears to be faster in active IBD. Pseudopolyps are a source of regeneration within the epithelium and, as shown here, have a faster proliferative drive than background mucosa in IBD patients. Pseudopolyps are not genetically inert and are a potential source of protumourigenic mutations in UC. Hence, pseudopolyps are a potential reservoir within the inflamed epithelium where mutations are harboured and where there is no competition from neighbouring epithelium, as it has been denuded following previous inflammation. MiRNA expression in pseudopolyps differs from that of UC-dysplasia and mucosa. In particular, the MiR-29 family was downregulated in pseudopolyps, a miRNA family that has been implicated in intestinal fibrosis formation in stricturing Crohn’s disease. Pseudopolyps have been traditionally thought of as benign, genetically inert and incidental findings characteristic of chronic inflammation. My research runs counter to this view indicating an exciting paradigm shift in the way we consider pseudopolyps, which may eventually alter the endoscopic management of these lesions in the future.

Inflammatory bowel disease (IBD) alters neuronal regulation of the gastrointestinal (GI) tract. The superior mesenteric ganglia (SMG) contain sympathetic neurons that modulate GI functions such, as motility and blood flow. IBD reduces the release of noradrenaline, a sympathetic neurotransmitter. We hypothesized that the reduction in NA release is due to inhibition of voltage-gated calcium current (ICa), as calcium influx is a regulator of neurotransmitter release. We also hypothesized that tumor necrosis factor α (TNFα), a proinflammatory cytokine elevated during IBD, can also inhibit the ICa of SMG neurons. Therefore, we compared ICa amplitude in neurons from normal mice and mice with dextran sulphate sodium (DSS; 5% w/v)-induced colitis. Neurons dissociated from the SMG were cultured overnight and changes to ICa were investigated using electrophysiological, Ca2+ imaging, PCR and neurotransmitter release techniques. Colitis significantly reduced ICa of SMG neurons by selectively inhibiting N-type Ca2+ channels. This was accompanied by a reduction in mRNA encoding the N-type channel alpha subunit (CaV 2.2) and a rightward shift in the voltage dependence of activation of ICa. Colitis reduced the NA release from the colon and jejunum. Depolarization-induced release of tritiated-NA was inhibited by ω-Conotoxin GVIA (300 nM). These results suggest that the changes in VGCC observed at the cell bodies of SMG neurons were also occurring at the nerve terminals during colitis. Similar experimental techniques were performed using SMG neurons incubated overnight in TNFα (1nM). TNFα decreased ICa and depolarization-induced Ca2+ influx in SMG neurons. Similar to DSS-induced colitis, the reduction in ICa was limited to N-type Ca2+ channels. Preincubation of neurons with SC 514 (20μM) and Bay 11 7082 (1µM), inhibitors of nuclear factor kappa B signaling, prevented the reduction in ICa. Preincubation with the p38 MAPK inhibitor, PD 169316 (30µM), recovered a smaller portion of the reduction in Ca2+ influx. These data suggest that DSS colitis and TNFα inhibit N-type VGCC ICa in sympathetic neurons and identify a novel role for NF-κB and p38 MAPK in the regulation of neurotransmitter release. These findings also suggest that DSS colitis inhibits NA release by altering sympathetic N-type VGCC in the colon and jejunum. / Thesis (Master, Physiology) -- Queen's University, 2008-09-02 12:06:20.438

Changes to the composition and function of the gut mononuclear phagocyte (MNP) compartment are associated with the development of intestinal inflammation. Much work has focused on the role of MNPs in gut-associated lymphoid tissue in maintaining homeostasis, however little is known regarding the roles of MNPs during colitis. We have investigated MNPs in the large intestinal lamina propria during the steady state and inflammation. One of our primary aims was to determine the contribution of MNP subsets to intestinal pathology. For our studies of inflammation, we focused mainly on the Helicobacter hepaticus infection + anti-IL-10R model, which induces inflammation of the colon and caecum (typhlocolitis). We defined the composition of the MNP compartment alongside intestinal pathology scores throughout Hh + anti-IL-10R typhlocolitis. Peak pathology, 2-3 weeks after induction of colitis, coincided with peak frequencies of CX₃CR1^int Ly6C^+ MNPs. Having observed the accumulation of CX₃CR1^int CD64^+ monocyte/macrophage MNPs in the inflamed lamina propria, we conducted comparative whole genome microarray analysis of these cells isolated from the large intestine three weeks after Hh + anti-IL-10R treatment. CX₃CR1^int CD64^+ MNPs selectively expressed a variety of pro- and anti-inflammatory genes, including a number of genes which individually can both promote and negatively regulate inflammation. IL-23 is essential for Hh + anti-IL-10R-induced intestinal pathology. We investigated the role of MNPs as a source of IL-23 which drives Hh + anti-IL-10R colitis. Unexpectedly, our results indicate that normally hyporesponsive CX₃CR1^hi macrophages may act as the initial source of IL-23, which induces development of colitis. Recruitment of Ly6C^+ MHCII^+ MNPs to the lamina propria was IL-23-dependent, and these cells also expressed IL-23, which may establish a positive feedback loop of immune cell recruitment, activation and IL-23 production. Finally, we also examined how MNPs might be recruited to the colonic lamina propria during inflammation. Our studies support the conclusion that CCR6 is not required for accumulation of monocyte-derived populations in the inflamed intestine. We cannot rule out a role for CCR2, however preliminary data from the Hh + anti-IL-10R colitis model suggest a potential role for CCR1 or its close relation CCRL2. Such pathways could represent new therapeutic targets in inflammatory bowel disease.