Gastroenterology

Gastroenterology

Volume 134, Issue 3, March 2008, Pages 768-780.e2
Gastroenterology

Basic–Alimentary Tract
Chronic Enteric Salmonella Infection in Mice Leads to Severe and Persistent Intestinal Fibrosis

https://doi.org/10.1053/j.gastro.2007.12.043Get rights and content

Background & Aims: Intestinal fibrosis and stricture formation are serious complications of Crohn’s disease, often requiring surgical intervention. Unfortunately, the mechanisms underlying intestinal fibrosis development are poorly understood, in part because of the lack of relevant animal models. Here, we present a novel murine model of severe and persistent intestinal fibrosis caused by chronic bacterial-induced colitis. Methods: Mice were treated with streptomycin 24 hours prior to oral infection with Salmonella enterica serovar Typhimurium. Tissues were analyzed for bacterial colonization and inflammation, and fibrosis was assessed by Masson’s trichrome staining and collagen quantification. Expression of the profibrotic cytokines transforming growth factor-β1, connective tissue growth factor and insulin-like growth factor-I was determined, and the cell types present in fibrotic tissues were assessed by immunohistochemistry. Results: Infection led to chronic Salmonella colonization of the cecum and colon followed by edema, mucosal ulcerations, and severe transmural inflammation. This pathology was accompanied by significantly elevated expression of transforming growth factor-β1, connective tissue growth factor, and insulin-like growth factor-I along with extensive type I collagen deposition in the cecal mucosa, submucosa, and muscularis mucosa of infected mice. Fibrosis was evident by 7 days postinfection, peaking at day 21 and still present at day 70. The fibrotic regions were found to be rich in fibroblasts and myofibroblasts. Conclusions: These data demonstrate that chronic Salmonella infection of the murine gastrointestinal tract leads to severe tissue fibrosis. Because this model is highly reproducible and easy to perform, it provides great potential for investigating both host and bacterial contributions to intestinal fibrosis.

Section snippets

Mice

129SvJ mice15 were bred in the Animal Unit at the University of British Columbia (UBC). 129Sv/ImJ, DBA2, and C3H/HeOuJ mice (Jackson Laboratories, Bar Harbor, ME) were infected at an age of 8–12 weeks. Mice were given 20 mg of streptomycin orally 24 hours prior to infection with 3 × 106 or 3 × 108 bacteria in 100 μL HEPES buffer (100 mmol/L, pH 8.0) by oral gavage. All animal experiments were conducted consistent with the ethical requirements of the Animal Care Committee at UBC.

Bacterial Strains

S Typhimurium

Chronic Infection With S Typhimurium Induces Inflammation and Tissue Pathology

Pretreatment with the antibiotic streptomycin facilitates S Typhimurium infection of the murine GI tract.13 129Sv/J mice were treated with streptomycin 24 hours prior to infection with 3 × 106S Typhimurium and killed at specific time points thereafter. By day 7 postinfection (pi), the ceca and colons of infected mice were heavily colonized, with the pathogen burden ranging from 105 to 109Salmonella in these tissues (Figure 1A), which is in line with previous studies.14 Colonization of all

Discussion

Intestinal fibrosis and stricture formation are among the most problematic clinical features of CD, in large part because they are strikingly resistant to anti-inflammatory treatments. As a result, therapeutic options are limited, with endoscopic balloon dilatation usually only delaying intervention with stricturoplasty or surgical resection of affected segments. Although the etiology underlying the development of intestinal fibrosis remains unknown, commensal bacteria and/or bacterial products

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    Supported by CIHR (to B.A.V. and B.B.F.) and Genome Canada (to B.B.F.); by postdoctoral fellowships from the Michael Smith Foundation for Health Research (MSFHR), Genome Canada, and the Deutsche Forschungsgemeinschaft (to G.A.G.); and by a doctoral fellowship from MSFHR (to K.S.B.B.).

    The authors thank Caixia Ma, Tina Huang, and Lisa Thorson for excellent technical assistance; Erin Boyle, Kelly McNagny, Kevan Jacobson, Michael Blennerhassett, and members of the Finlay lab for critical comments on the manuscript; and Carrie Rosenberger and Alan Aderem for kindly providing the flagellin mutant.

    Conflicts of interest: No conflicts of interest exist.

    1

    B.A.V. is the CHILD Foundation Research Scholar, the Canada Research Chair in Pediatric Gastroenterology, and an MSFHR Scholar.

    2

    B.B.F. is a CIHR Distinguished Investigator, an HHMI International Research Scholar, and the UBC Peter Wall Distinguished Professor.

    3

    G.A.G. and Y.V. contributed equally to this work.

    4

    B.A.V. and B.B.F. are co-senior authors.

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