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No description available.

Background: Several environmental risk factors have been implicated in the pathogenesis ofinflammatory bowel disease (IBD) and might cause an altered barrier function, a hallmark ofIBD. Recent evidence suggests that patients with late-onset ulcerative colitis (UC) have anincreased serum level of perfluoroalkyl substances (PFAS), one of the major chemical groupscontaminating our diet. A potential route via which PFAS might contribute to the disease is bydisrupting the intestinal barrier. However, whether intake of PFAS dose induce an increasedintestinal permeability is still unknown. Aim: The aim of the thesis is to investigate the effect of in vivo exposure toperfluorooctanesulfonic acid (PFOA) in mice on colon barrier function. The hypothesis is thatlong time exposure to PFOA contributes to the development of late-onset ulcerative colitis bydisrupting the intestinal barrier. Methods: This controlled laboratory study used 7 mice exposed to PFOA in vivo via thedrinking water for 3 weeks and a control group of 9 mice for reference. Colon tissue from themice were excised for assessing intestinal permeability using the Ussing chamber method.FITCH-dextran was used as a macromolecular probe in the Ussing chamber to investigate themucosal-serosal flux across the intestinal mucosa to see macromolecular permeability andelectrophysiological parameters were assessed to investigate tight junction permeability,stimulated secretory response to Carbachol and active ion transport. Results: Although there were no statistically significant results between the PFOA treated groupand the control group, a trend of increased secretory response to Carbachol was observed in thePFOA group compared to the controls. Conclusion: The study demonstrates that in vivo exposure to PFOA does not induce an alteredintestinal barrier in terms of electrophysiological parameters and macromolecular flux. Futureexperiments are needed with a larger population and potentially genetically predisposed mice.Key

<p>Current gold standard practices for the diagnosis of tissue disease involve invasive tissue biopsies subjected to a time consuming histopathological examination process. An optical biopsy can offer a non-invasive diagnostic alternative by exploiting the properties of naturally occurring light-tissue interactions. A time-resolved fluorescence spectroscopy instrument (355 nm excitation) has previously been developed by our lab to capture the fluorescence response of gastrointestinal tissue (370-550 nm in 5 nm increments, 25 ns at 1000 ps/pt). Measurements were conducted ex-vivo during routine upper gastrointestinal tract biopsies on duodenum, antrum, stomach body, and esophageal tissue. The work currently presented is focused on protocol development for tissue handling, measurement collection, clinical data management, fluorescent decay modeling using Laguerre based deconvolution, instrument performance evaluation, and k-means based classification.</p> <p>Descriptive parameters derived from spectral (total signal intensity) and temporal (lifetime and Laguerre polynomial coefficients) analysis were used to evaluate the data. It was found that data were only compromised when the total signal intensity for the peak wavelength 455 nm fell blow 19.5 V·ns. The data did not exhibit any signs of photobleaching or pulse width broadening that would have otherwise distorted the lifetime from its true fluorescence response. Data for diseased tissue were limited so the clinical diagnosis was used to classify normal duodenum tissue from normal esophageal tissue. Over 400 pairs of parameters demonstrated k-means can identify duodenum tissue with 87.5 % sensitivity and 87.5 % specificity or better. With some dimensional axis transformations these results could be improved. The lifetimes are not factors here but the relative intensity and decay shape were. Protocols can be applied to diseased or other tissue types with little adaptation. Just a single set of parameters may hold the key to help surgeons choose optimum locations for traditional biopsies or perhaps one day replace them altogether.</p> / Master of Applied Science (MASc)

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The gastrointestinal (GI) tract is a crucial interface for the host, food derived antigens, the commensal microbiota and invasive pathogens. Here, the immune system must simultaneously protect against harmful pathogens and remain tolerogenic to commensal bacteria and nutrients. The intestinal mucosa of adult humans and mice is enriched for innate lymphoid cells (ILCs) that express the transcription factor RORγt (ILC3s). These cells are crucial for maintaining the delicate balance of tolerance and immunity in the GI tract. They serve protective roles in immune responses to infectious organisms, are essential for the formation of lymphoid tissues, and help maintain gut homeostasis via signaling to epithelial cells through interleukin 22 (IL-22). ILC3s in the GI tract can be further categorized into three main subsets with distinct and overlapping functional roles. These subsets can be identified by either the expression of CCR6, Nkp46, or by lacking both markers- double negative (DN), some of which also make IL-17A. Signals that mediate the development and function of the various ILC3 subsets are still an area of active investigation. Notch signaling is a highly conserved pathway that contributes to the development and function of many types of immune cells. There has been some investigation into the role Notch signaling plays in the development of ILC3, particularly in the transition from DN to Nkp46 ILC3. However, all three subsets of ILC3s express two Notch receptor isoforms (Notch1 and Notch2) the individual roles of these two receptors have not been dissected. We show signaling through Notch1 and Notch2 individually contribute to Nkp46 ILC3 development in a cell intrinsic manner. We also show Notch signaling, primarily through Notch2, reinforces the ILC3 program and suppresses the ILC1-like program in Nkp46 ILC3 by promoting the expression of RORγt, c-Maf, and IL-22, and suppressing the expression of T-bet and IFNγ. Notch signaling also supports ILC3-identity genes in CCR6 ILC3, promoting RORγt, IL-17A, and IL-22. We, therefore, identify a novel role for Notch signaling in ILC3 function. As such, Notch-deficient ILC3 fail to initiate proper immune response to enteric pathogen Citrobacter rodentium, leading to more severe infection. Our results show how a highly conserved signaling pathway contributes to ILC3 development, identity, and function. The GI tract is also enriched with helper CD4 T cells that express RORγt, IL-17A, and IL-22 (Th17), which share many phenotypic and functional features with ILC3. The relative contribution of ILC3 and Th17 cells to immune phenotypes remains poorly understood. Moreover, due to the lack of ILC3-specific depletion models, how ILC3 regulate mucosal protection in the presence of Th17 cells is not clear. Here, we examined non-redundant functions of ILC3 in intestinal immunity using novel ILC3-deficient mice that maintain endogenous T cells, Th17 cells, and secondary lymphoid organs. ILC3 depletion did not affect IL-22-production by CD4 T cells during homeostasis. However, despite the presence of IL-22-producing T cells, ILC3 and ILC3- derived IL-22 were required for maintaining homeostatic functions of the intestinal epithelium. ILC3 were dispensable for generation of Th17 and Th22 cell responses to pathogenic bacteria, though Th17 and Th22 responses were delayed in the absence of ILC3. ILC3- deficient mice were capable of pathogen clearance and survived infection with low dose Citrobacter rodentium in the presence of antigen-specific Th17 cells. However, ILC3 increased pathogen tolerance at early timepoints of infection by activating tissue-protective immune pathways. Consequently, ILC3 were indispensable for survival of high dose infection. We also assess the role of ILC3 and Th17 cell in metabolic syndrome, using our novel model. Our lab demonstrated commensal-specific Th17 cells are protective against metabolic syndrome and lost under high-fat, high-sugar diet. ILC3s drive the expansion of a commensal member, Faecalibaculum rodentium (F. rod), which displaces the Th17 cell-inducing commensal, segemented filamentous bacteria (SFB). Without ILC3s, SFB is not lost from the microbiota, commensal- specific Th17 cells are maintained and there is, therefore, no development of metabolic syndrome. Our results demonstrate crucial context- dependent roles for ILC3 in immune-sufficient animals during homeostasis, infection, and metabolic disease.

The human body is home to complex microbial communities that are fundamental to our physiology. Utilizing mouse models, behavior assays, gene expression analyses, and probiotic interventions, this research explores the intricate relationship between the gut microbiome, the central nervous system, and the immune system. I discuss a strain of Escherichia coli Nissle engineered to produce serotonin, revealing its impact on gut function and immune response. I also evaluate butyrate’s potential to alleviate symptoms of Fragile X Syndrome, highlighting the gut-brain axis. Additionally, I study a strain of Bifidobacterium adolescentis and its role in metabolizing bile acids and modulating host immune cells and stress. Collectively, these studies address the complex interplay between the gut microbiome and host health and behavior, illuminating the therapeutic potential of microbiome manipulation and setting the stage for novel interventions in neurodevelopmental disorders and immune function regulation.