Lack of Effect of Murine Norovirus Infection on a Mouse Model of Bacteria-Induced Colon Cancer

Murine norovirus (MNV) is endemic in mouse research facilities in the United States and Europe, with a prevalence as high as 58% to 64%. Because of MNV's orofecal route of infection, clinically silent persistent infections in some mouse strains, and proclivity for macrophage and dendritic cells, its presence in mouse colonies has potential to alter phenotypes in experimental mouse models, particularly those involving inflammation and immunologic responses. Although MNV is subclinical, not causing overt disease in immunocompetent mice, we found that MNV infection can accelerate bacteria-induced inflammatory bowel disease (IBD) progression in Mdr1a^(-/-) mice. The studies presented here examined whether MNV infection also affects the phenotype of a bacterially driven mouse model of inflammation-associated colon cancer in genetically susceptible Smad3^(-/-) mice. In vitro culture of bone-marrow—derived macrophages (BMDM) was used to determine whether MNV4 influenced macrophage cytokine production. For in vivo studies, Smad3-/- mice were infected with MNV4 one week prior to infection with Helicobacter. Mice were monitored for 17 to 32 wk for development of IBD and colon cancer, and tissues were analyzed histopathologically. Although in vitro infection of BMDM with MNV4 led to increased inflammatory cytokine production, infection with MNV4 in vivo did not result in any statistically significant differences in survival, IBD scores, tumor incidence, or tumor phenotype in Smad3^(-/-) mice. In addition, MNV infection alone did not result in IBD or colon cancer. Therefore MNV infection alone or in conjunction with Helicobacter does not alter the development or progression of IBD or colon cancer in Smad3^(-/-) mice

Murine Norovirus: An Intercurrent Variable in a Mouse Model of Bacteria-Induced Inflammatory Bowel Disease

Murine norovirus (MNV) has recently been recognized as a widely prevalent viral pathogen in mouse colonies and causes disease and mortality in mice with impaired innate immunity. We tested the hypothesis that MNV infection would alter disease course and immune responses in mice with inflammatory bowel disease (IBD). FVB.129P2-Abcb1a^(tm1Bor) N7 (Mdr1a−/−) mice develop spontaneous IBD that is accelerated by infection with Helicobacter bilis. As compared with controls, Mdr1a−/− mice coinfected with MNV4 and H. bilis showed greater weight loss and IBD scores indicative of severe colitis, demonstrating that MNV4 can modulate the progression of IBD. Compared with controls, mice inoculated with MNV4 alone had altered levels of serum biomarkers, and flow cytometric analysis of immune cells from MNV4-infected mice showed changes in both dendritic cell (CD11c+) and other nonT cell (CD4− CD8−) populations. Dendritic cells isolated from MNV4-infected mice induced higher IFNγ production by polyclonal T cells in vitro at 2 d after infection but not at later time points, indicating that MNV4 infection enhances antigen presentation by dendritic cells early after acute infection. These findings indicate that acute infection with MNV4 is immunomodulatory and alters disease progression in a mouse model of IBD

ALDH1A Inhibition Suppresses Colitis and Alters α4β7 Integrin Expression on Activated T Cells in <i>Mdr1a</i>^−/− Mice

There are limited pharmacological treatment options for inflammatory bowel disease (IBD), and some of these options are expensive and administered by injection or infusion. Thus, new cheaper and easier (oral) treatment options are needed. ALDH1A enzymes produce retinoic acid that can affect intestinal diseases such as IBD by regulating immune cells in the gut. We previously demonstrated that an orally deliverable ALDH1A inhibitor, WIN 18,466, can suppress colitis in an acute mouse model of IBD. Here, we tested the efficacy of ALDH1A inhibition in a chronic mouse model of IBD. Mdr1a−/− mice were treated with a diet containing WIN 18,446 starting 1 week prior to inducing colitis by H. bilis inoculation. Treatment was continued until the study end point and colitis was monitored based on clinical symptoms and confirmed by histological analysis. Immune cell phenotypes in colon-draining lymph nodes (cMLN) were analyzed. WIN 18,446 treatment reduced clinical symptoms and improved histopathologic colitis scores. This was associated with decreased expression of the gut homing integrin, α4β7, on T cells in cMLN; increased expression of CD103, a protein associated with tissue-resident memory T cells; and changes in dendritic cells, plasmacytoid dendritic cells and B cells in inhibitor-treated mice. ALDH1A inhibition broadly influences immune cells during colitis and is a potential new target for IBD treatment. Future studies will be needed to determine the efficacy of ALDH1A inhibition on active colitis and to evaluate its relative efficacy in comparison to approved drugs

Characterization of Dextran Sodium Sulfate-Induced Inflammation and Colonic Tumorigenesis in <i>Smad3</i>^−/− Mice with Dysregulated TGFβ

<div><p>There are few mouse models that adequately mimic large bowel cancer in humans or the gastrointestinal inflammation which frequently precedes it. Dextran sodium sulphate (DSS)-induces colitis in many animal models and has been used in combination with the carcinogen azoxymethane (AOM) to induce cancer in mice. <i>Smad3</i>^−/− mice are deficient in the transforming growth factor beta (TGFβ) signaling molecule, <i>SMAD3</i>, resulting in dysregulation of the cellular pathway most commonly affected in human colorectal cancer, and develop inflammation-associated colon cancer. Previous studies have shown a requirement for a bacterial trigger for the colitis and colon cancer phenotype in <i>Smad3^−/−</i> mice. Studies presented here in <i>Smad3^−/−</i> mice detail disease induction with DSS, without the use of AOM, and show a) <i>Smad3</i>^−/− mice develop a spectrum of lesions ranging from acute and chronic colitis, crypt herniation, repair, dysplasia, adenomatous polyps, disseminated peritoneal adenomucinosis, adenocarcinoma, mucinous adenocarcinoma (MAC) and squamous metaplasia; b) the colon lesions have variable galactin-3 (Mac2) staining c) increased DSS concentration and duration of exposure leads to increased severity of colonic lesions; d) heterozygosity of <i>SMAD3</i> does not confer increased susceptibility to DSS-induced disease and e) disease is partially controlled by the presence of T and B cells as <i>Smad3</i>^−/−<i>Rag2</i>^−/− double knock out (DKO) mice develop a more severe disease phenotype. DSS-induced disease in <i>Smad3</i>^−/− mice may be a useful animal model to study not only inflammation-driven MAC but other human diseases such as colitis cystica profunda (CCP) and pseudomyxomatous peritonei (PMP).</p></div