Bacteroides fragilis are common colonic commensals, known to occupy a mucosal niche in the colon and the leading anaerobe in human disease. One class of B. fragilis, enterotoxigenic Bacteroides fragilis (ETBF), is recently recognized as an etiology of inflammatory diarrheal disease and may incite active inflammatory bowel disease. Up to 30% of individuals, however, may be colonized, seemingly asymptomatically, with ETBF. The primary virulence factor of ETBF is a 20 kDa zinc-dependent metalloprotease toxin termed B. fragilis toxin (BFT). Our new ETBF-infected conventional C57BL/6 mouse model reveals that mice colonized with ETBF develop rapid onset symptomatic colitis (within 3 days) with marked colitis at 1 to 2 weeks. The colonic inflammatory infiltrates at 1 week are composed of increased CD4+ T cells that produce interleukin-17 (IL-17) but not ?-interferon or IL-4. Both the colonic epithelial cells and a subset of mucosal inflammatory cells display phosphorylated signal transducer and activator of transcription-3 (Stat3). Over time ETBF acute colitis subsides yielding chronic colitis that persists at least 8 months. Using matched isogenic B. fragilis strains differing only in their secretion of biologically active BFT, the colitis can be ascribed, at least in part, to BFT. In vitro BFT increases intestinal epithelial permeability at least, in part, by cleavage of the zonula adherens protein, E-cadherin, and activates Nuclear Factor-?B signaling resulting in secretion of the proinflammatory cytokine, interleukin-8. Our data support the hypothesis that ETBF colonization stimulates acute colitis mediated by induction of innate responses that direct adaptive responses along a Th17 pathway dependent on Stat3 signaling. We postulate that ETBF induce a continuum of human pathology from `asymptomatic'colonization, potentially associated with colonic hyperplasia and inflammation (precursor conditions to neoplastic transformation), to inflammatory diarrhea and colitis. The goals of this proposal are to identify the innate and adaptive host immune mechanisms associated with initiation and persistence of ETBF-induced colitis in C57BL/6 mice. We will define the contribution of Th17 effector cells and Stat signaling to the inflammatory response in ETBF-induced colitis. Our results allow us to use a common human colonic bacterium, ETBF, to begin to understand the newly recognized Th17-dependent colonic inflammation, potentially providing insights into therapeutic approaches for a common clinical problem, colitis.

Public Health Relevance

Colonic inflammation (colitis) contributes to a large burden of disease including two major public health concerns. The first is infectious diarrheal diseases, a global cause of morbidity and mortality that is associated with malnutrition and delayed cognitive development in children;and the second is colorectal cancer, the second leading cause of cancer-related mortality in the United States. Understanding colonic inflammation may also help in identifying treatments for individuals afflicted by inflammatory bowel disease (Crohn's disease and ulcerative colitis) and irritable bowel syndrome, an illness disproportionately affecting women.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK080817-05
Application #
8230685
Study Section
Gastrointestinal Mucosal Pathobiology Study Section (GMPB)
Program Officer
Grey, Michael J
Project Start
2008-05-01
Project End
2013-02-28
Budget Start
2012-03-01
Budget End
2013-02-28
Support Year
5
Fiscal Year
2012
Total Cost
$341,564
Indirect Cost
$133,293
Name
Johns Hopkins University
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
001910777
City
Baltimore
State
MD
Country
United States
Zip Code
21218
Wick, Elizabeth C; Rabizadeh, Shervin; Albesiano, Emilia et al. (2014) Stat3 activation in murine colitis induced by enterotoxigenic Bacteroides fragilis. Inflamm Bowel Dis 20:821-34
McAllister, Florencia; Housseau, Franck; Sears, Cynthia L (2014) Microbiota and immune responses in colon cancer: more to learn. Cancer J 20:232-6
Dejea, Christine; Wick, Elizabeth; Sears, Cynthia L (2013) Bacterial oncogenesis in the colon. Future Microbiol 8:445-60
Sears, Cynthia L (2012) In celebration of Sydney M. Finegold, M.D.: bacteroides fragilis in the colon: the good & the bad. Anaerobe 18:192-6
O'Hagan, Heather M; Wang, Wei; Sen, Subhojit et al. (2011) Oxidative damage targets complexes containing DNA methyltransferases, SIRT1, and polycomb members to promoter CpG Islands. Cancer Cell 20:606-19
Goodwin, Andrew C; Destefano Shields, Christina E; Wu, Shaoguang et al. (2011) Polyamine catabolism contributes to enterotoxigenic Bacteroides fragilis-induced colon tumorigenesis. Proc Natl Acad Sci U S A 108:15354-9
Sears, Cynthia L; Pardoll, Drew M (2011) Perspective: alpha-bugs, their microbial partners, and the link to colon cancer. J Infect Dis 203:306-11
Banerjee, Arup; Meyer, Keith; Mazumdar, Budhaditya et al. (2010) Hepatitis C virus differentially modulates activation of forkhead transcription factors and insulin-induced metabolic gene expression. J Virol 84:5936-46
Housseau, Franck; Sears, Cynthia L (2010) Enterotoxigenic Bacteroides fragilis (ETBF)-mediated colitis in Min (Apc+/-) mice: a human commensal-based murine model of colon carcinogenesis. Cell Cycle 9:3-5
Wick, Elizabeth C; Sears, Cynthia L (2010) Bacteroides spp. and diarrhea. Curr Opin Infect Dis 23:470-4

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