Inflammatory bowel diseases (IBD) Crohn's Disease (CD) and Ulcerative Colitis (UC) are associated with substantial health burden in the United States. It is also knownthat IBD patients have elevated mucosal immune responses to the enteric microflora. Active flares of IBD are associated with, and thought to be mediated by, innate immunity, specifically neutrophil infiltration to the intestinalmucosa. Conversely, the chronicphase of IBD is associated with, and maintained by, the increased mucosal presence of adaptive immune cells with a particularly important role for CD4+ T- cells. Several recent observations indicate that one underlying cause of such IBD-associated immune responses may be mutations in genes that mediate innate immunity. However, it is unclear whether the primary consequence of such mutations is loss or gain of innate immune function. Bacterial protein flagellin, the monomeric subunit of flagella, is a dominant innate immune activator of intestinal epithelial cells. My CCFA Research Fellowship sought to define the role of innate immunity to flagellin in murine models of gut inflammation. We hypothesized that mice lacking the flagellin receptor, toll-like receptor 5 (TLR5), might be protected from developing chronic inflammation. In contrast, we observed, that mice engineered to lack TLR5 develop spontaneous colitis. We hypothesize that TLR5KO colitis results from an inability to control the commensal microflora,which results in activation of TLR4 and other innate immune signaling pathways. However, our most recent observations suggest that such alterations are not sufficient to drive robust colitis in TLR5KO mice. Rather, we have preliminarily observed that TLR5KO colitis is associated with, and requires, alterations in adaptive immunity. We hypothesize that loss of TLR5 on gut epithelial cells results in lymphocytes acquiring a colitiogenic profile, which amplifies and sustains the inflammation triggered by activation of innate immunity. Alternatively, in light of the ambiguityregarding the role of TLR5 on antigen-presenting cells (APC) and increasing appreciation that TLRs can be expressed on T-cells, we will also consider the possibility that loss of TLR5 on APC and/or T-cells results in a dysregulated adaptive immune response. We propose to investigate these hypotheses by examining the alterations in adaptive immunity in TLR5K.Omice and defining which of these alterations are necessary and/or sufficient to drive colitis. In addition to advancing the understanding of innate-immune interactions in the gut, an area germane to the pathogenesis of IBD, the immunology, I will learn from executing these aims should greatly aid my long term potential as an IBD researcher.

Public Health Relevance

This study proposed should delineate importance of adaptive immunity in innate immune deficient mouse colitis model. It will shed light on the crosstalk between innate and adaptive immunity that ultimately culminates in spontaneous colitis.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Scientist Development Award - Research & Training (K01)
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Diabetes, Endocrinology and Metabolic Diseases B Subcommittee (DDK)
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Podskalny, Judith M,
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Georgia State University
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Singh, Vishal; Kumar, Manish; San Yeoh, Beng et al. (2016) Inhibition of Interleukin-10 Signaling Induces Microbiota-dependent Chronic Colitis in Apolipoprotein E Deficient Mice. Inflamm Bowel Dis 22:841-52
Singh, Vishal; Yeoh, Beng San; Chassaing, Benoit et al. (2016) Microbiota-inducible Innate Immune, Siderophore Binding Protein Lipocalin 2 is Critical for Intestinal Homeostasis. Cell Mol Gastroenterol Hepatol 2:482-498.e6
Singh, Vishal; Yeoh, Beng San; Carvalho, Frederic et al. (2015) Proneness of TLR5 deficient mice to develop colitis is microbiota dependent. Gut Microbes 6:279-83
Singh, Vishal; Yeoh, Beng San; Xiao, Xia et al. (2015) Interplay between enterobactin, myeloperoxidase and lipocalin 2 regulates E. coli survival in the inflamed gut. Nat Commun 6:7113
Singh, Vishal; Chassaing, Benoit; Zhang, Limin et al. (2015) Microbiota-Dependent Hepatic Lipogenesis Mediated by Stearoyl CoA Desaturase 1 (SCD1) Promotes Metabolic Syndrome in TLR5-Deficient Mice. Cell Metab 22:983-96
Chassaing, Benoit; Kumar, Manish; Baker, Mark T et al. (2014) Mammalian gut immunity. Biomed J 37:246-58
Chassaing, Benoit; Aitken, Jesse D; Malleshappa, Madhu et al. (2014) Dextran sulfate sodium (DSS)-induced colitis in mice. Curr Protoc Immunol 104:Unit 15.25.
Rogers, Connie J; Prabhu, Kumble Sandeep; Vijay-Kumar, Matam (2014) The microbiome and obesity-an established risk for certain types of cancer. Cancer J 20:176-80
Shashidharamurthy, Rangaiah; Machiah, Deepa; Aitken, Jesse D et al. (2013) Differential role of lipocalin 2 during immune complex-mediated acute and chronic inflammation in mice. Arthritis Rheum 65:1064-73
Chassaing, Benoit; Srinivasan, Gayathri; Delgado, Maria A et al. (2012) Fecal lipocalin 2, a sensitive and broadly dynamic non-invasive biomarker for intestinal inflammation. PLoS One 7:e44328

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