Genetic analysis of susceptibility to dextran sulfate sodium-induced colitis in mice

Tofacitinib fails to prevent T cell transfer colitis in mice but ameliorates disease activity

Tofactinib is a JAK inhibitor approved for ulcerative colitis in humans. Despite of its' proven effectiveness in humans, mechanistic data are scarce on the effectiveness of Tofactinib in experimental colitis in mice. We induced experimental colitis by transfer of CD4+CD25- isolated T cells into RAG2-/- (T and B cell deficient) mice and treated these mice with tofacitinib for 5-6 weeks either with a dosage of 10 or 40 mg/kg body weight immediately after CD4+ transfer or started treatment after first symptoms of disease for several weeks. While treatment with tofacitinib immediately after transfer resulted in an enhanced expansion of CD4+ T cells and did not prevent occurrence of colitis, treatment after start of symptoms of colitis ameliorated disease activity on a clinical basis and in histological analyses. Tofacitinib is effective in the treatment of murine experimental T cell transfer colitis, however does not prevent occurrence of disease.

Antibody-Mediated Delivery of VEGFC Ameliorates Experimental Chronic Colitis

Crohn's disease (CD) and ulcerative colitis (UC) are two distinct forms of inflammatory bowel disease (IBD) characterized by an expanded lymphatic network with impaired functionality both in mouse models and in human patients. In this study, we investigated whether targeted delivery of the pro-lymphangiogenic vascular endothelial growth factor C (VEGFC) to the site of inflammation may represent a new, clinically feasible strategy for treating IBD. To achieve targeting of inflamed tissue, we developed a fusion protein consisting of human VEGFC fused to the F8 antibody (F8-VEGFC), which specifically binds to the extradomain A (EDA) of fibronectin, a spliced isoform almost exclusively expressed in inflamed tissues. The therapeutic activity of intravenously administered F8-VEGFC, compared to a targeted construct lacking VEGFC (F8-SIP), was investigated in a mouse model of dextran sodium sulfate (DSS)-induced colitis. The presence of EDA fibronectin was detected in both human and mouse inflamed colon tissue. Biodistribution studies of radiolabeled F8-VEGFC revealed a specific accumulation of the antibody in the colon of DSS-administered mice, as compared to an untargeted VEGFC fusion protein (KSF-VEGFC) (binding the irrelevant hen egg lysozyme antigen). Systemic treatment with F8-VEGFC significantly reduced the clinical and histological signs of inflammation, expanded the lymphatic vascular network, reduced the density of immune cells, and also decreased the expression of inflammatory cytokines in the inflamed colon. Overall, these results reveal that administration of F8-VEGFC represents a novel and promising approach for the treatment of IBD.

Intestinal Organoids as a Novel Complementary Model to Dissect Inflammatory Bowel Disease

Inflammatory bowel diseases (IBDs) include colitis ulcerosa and Crohn's disease, besides the rare microscopic colitis. Both diseases show a long-lasting, relapsing-remitting, or even chronic active course with tremendous impact on quality of life. IBDs frequently cause disability, surgical interventions, and high costs; as in other autoimmune diseases, their prevalent occurrence at an early phase of life raises the burden on health care systems. Unfortunately, our understanding of the pathogenesis is still incomplete and treatment therefore largely focuses on suppressing the resulting excessive inflammation. One obstacle for deciphering the causative processes is the scarcity of models that parallel the development of the disease, since intestinal inflammation is mostly induced artificially; moreover, the intestinal epithelium, which strongly contributes to IBD pathogenesis, is difficult to assess. Recently, the development of intestinal epithelial organoids has overcome many of those problems. Here, we give an overview on the current understanding of the pathogenesis of IBDs with reference to the limitations of previous well-established experimental models. We highlight the advantages and detriments of recent organoid-based experimental setups within the IBD field and suggest possible future applications.

Mouse genome-wide association study identifies polymorphisms on chromosomes 4, 11, and 15 for age-related cardiac fibrosis

Dystrophic cardiac calcinosis (DCC), also called epicardial and myocardial fibrosis and mineralization, has been detected in mice of a number of laboratory inbred strains, most commonly C3H/HeJ and DBA/2J. In previous mouse breeding studies between these DCC susceptible and the DCC-resistant strain C57BL/6J, 4 genetic loci harboring genes involved in DCC inheritance were identified and subsequently termed Dyscalc loci 1 through 4. Here, we report susceptibility to cardiac fibrosis, a sub-phenotype of DCC, at 12 and 20 months of age and close to natural death in a survey of 28 inbred mouse strains. Eight strains showed cardiac fibrosis with highest frequency and severity in the moribund mice. Using genotype and phenotype information of the 28 investigated strains, we performed genome-wide association studies (GWAS) and identified the most significant associations on chromosome (Chr) 15 at 72 million base pairs (Mb) (P < 10(-13)) and Chr 4 at 122 Mb (P < 10(-11)) and 134 Mb (P < 10(-7)). At the Chr 15 locus, Col22a1 and Kcnk9 were identified. Both have been reported to be morphologically and functionally important in the heart muscle. The strongest Chr 4 associations were located approximately 6 Mb away from the Dyscalc 2 quantitative trait locus peak within the boundaries of the Extl1 gene and in close proximity to the Trim63 and Cap1 genes. In addition, a single-nucleotide polymorphism association was found on chromosome 11. This study provides evidence for more than the previously reported 4 genetic loci determining cardiac fibrosis and DCC. The study also highlights the power of GWAS in the mouse for dissecting complex genetic traits.

Innate Mucosal Immune System Response of BALB/c vs C57BL/6 Mice to Injury in the Setting of Enteral and Parenteral Feeding

BACKGROUND

Outbred mice exhibit increased airway and intestinal immunoglobulin A (IgA) following injury when fed normal chow, consistent with humans. Parenteral nutrition (PN) eliminates IgA increases at both sites. Inbred mice are needed for detailed immunological studies; however, specific strains have not been evaluated for this purpose. BALB/c and C57BL/6 are common inbred mouse strains but demonstrate divergent immune responses to analogous stress. This study addressed which inbred mouse strain best replicates the outbred mouse and human immune response to injury.

METHODS

Intravenously cannulated mice received chow or PN for 5 days and then underwent sacrifice at 0 or 8 hours following controlled surgical injury (BALB/c: n = 16-21/group; C57BL/6: n = 12-15/group). Bronchoalveolar lavage (BAL) was analyzed by enzyme-linked immunosorbent assay for IgA, tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-6, while small intestinal wash fluid (SIWF) was analyzed for IgA.

RESULTS

No significant increase in BAL IgA occurred following injury in chow- or PN-fed BALB/c mice (chow: P = .1; PN: P = .7) despite significant increases in BAL TNF-α and SIWF IgA (chow: 264 ± 28 vs 548 ± 37, P < .0001; PN: 150 ± 12 vs 301 ± 17, P < .0001). Injury significantly increased mucosal IgA in chow-fed C57BL/6 mice (BAL: 149 ± 33 vs 342 ± 87, P = .01; SIWF: 236 ± 28 vs 335 ± 32, P = .006) and BAL cytokines. After injury, PN-fed C57BL/6 mice exhibited no difference in BAL IgA (P = .9), BAL cytokines, or SIWF IgA (P = .1).

CONCLUSIONS

C57BL/6 mice exhibit similar airway responses to injury as outbred mice and humans, providing an appropriate model for studying mucosal responses to injury. The BALB/c mucosal immune system responds differently to injury and does not replicate the human injury response.

Integrative genetic analysis of allergic inflammation in the murine lung

Airway allergen exposure induces inflammation among individuals with atopy that is characterized by altered airway gene expression, elevated levels of T helper type 2 cytokines, mucus hypersecretion, and airflow obstruction. To identify the genetic determinants of the airway allergen response, we employed a systems genetics approach. We applied a house dust mite mouse model of allergic airway disease to 151 incipient lines of the Collaborative Cross, a new mouse genetic reference population, and measured serum IgE, airway eosinophilia, and gene expression in the lung. Allergen-induced serum IgE and airway eosinophilia were not correlated. We detected quantitative trait loci (QTL) for airway eosinophilia on chromosome (Chr) 11 (71.802-87.098 megabases [Mb]) and allergen-induced IgE on Chr 4 (13.950-31.660 Mb). More than 4,500 genes expressed in the lung had gene expression QTL (eQTL), the majority of which were located near the gene itself. However, we also detected approximately 1,700 trans-eQTL, and many of these trans-eQTL clustered into two regions on Chr 2. We show that one of these loci (at 147.6 Mb) is associated with the expression of more than 100 genes, and, using bioinformatics resources, fine-map this locus to a 53 kb-long interval. We also use the gene expression and eQTL data to identify a candidate gene, Tlcd2, for the eosinophil QTL. Our results demonstrate that hallmark allergic airway disease phenotypes are associated with distinct genetic loci on Chrs 4 and 11, and that gene expression in the allergically inflamed lung is controlled by both cis and trans regulatory factors.

The Collaborative Cross as a resource for modeling human disease: CC011/Unc, a new mouse model for spontaneous colitis

Inflammatory bowel disease (IBD) is an immune-mediated condition driven by improper responses to intestinal microflora in the context of environmental and genetic background. GWAS in humans have identified many loci associated with IBD, but animal models are valuable for dissecting the underlying molecular mechanisms, characterizing environmental and genetic contributions and developing treatments. Mouse models rely on interventions such as chemical treatment or introduction of an infectious agent to induce disease. Here, we describe a new model for IBD in which the disease develops spontaneously in 20-week-old mice in the absence of known murine pathogens. The model is part of the Collaborative Cross and came to our attention due to a high incidence of rectal prolapse in an incompletely inbred line. Necropsies revealed a profound proliferative colitis with variable degrees of ulceration and vasculitis, splenomegaly and enlarged mesenteric lymph nodes with no discernible anomalies of other organ systems. Phenotypic characterization of the CC011/Unc mice with homozygosity ranging from 94.1 to 99.8% suggested that the trait was fixed and acted recessively in crosses to the colitis-resistant C57BL/6J inbred strain. Using a QTL approach, we identified four loci, Ccc1, Ccc2, Ccc3 and Ccc4 on chromosomes 12, 14, 1 and 8 that collectively explain 27.7% of the phenotypic variation. Surprisingly, we also found that minute levels of residual heterozygosity in CC011/Unc have significant impact on the phenotype. This work demonstrates the utility of the CC as a source of models of human disease that arises through new combinations of alleles at susceptibility loci.

Induction of bacterial antigen-specific colitis by a simplified human microbiota consortium in gnotobiotic interleukin-10-/- mice

We evaluated whether a simplified human microbiota consortium (SIHUMI) induces colitis in germfree (GF) 129S6/SvEv (129) and C57BL/6 (B6) interleukin-10-deficient (IL-10(-/-)) mice, determined mouse strain effects on colitis and the microbiota, examined the effects of inflammation on relative bacterial composition, and identified immunodominant bacterial species in "humanized" IL-10(-/-) mice. GF wild-type (WT) and IL-10(-/-) 129 and B6 mice were colonized with 7 human-derived inflammatory bowel disease (IBD)-related intestinal bacteria and maintained under gnotobiotic conditions. Quantification of bacteria in feces, ileal and colonic contents, and tissues was performed using 16S rRNA gene selective quantitative PCR. Colonic segments were scored histologically, and gamma interferon (IFN-γ), IL-12p40, and IL-17 levels were measured in supernatants of unstimulated colonic tissue explants and of mesenteric lymph node (MLN) cells stimulated by lysates of individual or aggregate bacterial strains. Relative bacterial species abundances changed over time and differed between 129 and B6 mice, WT and IL-10(-/-) mice, luminal and mucosal samples, and ileal and colonic or fecal samples. SIHUMI induced colitis in all IL-10(-/-) mice, with more aggressive colitis and MLN cell activation in 129 mice. Escherichia coli LF82 and Ruminococcus gnavus lysates induced dominant effector ex vivo MLN TH1 and TH17 responses, although the bacterial mucosal concentrations were low. In summary, this study shows that a simplified human bacterial consortium induces colitis in ex-GF 129 and B6 IL-10(-/-) mice. Relative concentrations of individual SIHUMI species are determined by host genotype, the presence of inflammation, and anatomical location. A subset of IBD-relevant human enteric bacterial species preferentially stimulates bacterial antigen-specific TH1 and TH17 immune responses in this model, independent of luminal and mucosal bacterial concentrations.

Guanylate cyclase C deficiency causes severe inflammation in a murine model of spontaneous colitis

Background

Guanylate Cyclase C (GC-C; Gucy2c) is a transmembrane receptor expressed in intestinal epithelial cells. Activation of GC-C by its secreted ligand guanylin stimulates intestinal fluid secretion. Familial mutations in GC-C cause chronic diarrheal disease or constipation and are associated with intestinal inflammation and infection. Here, we investigated the impact of GC-C activity on mucosal immune responses.

Methods

We utilized intraperitoneal injection of lipopolysaccharide to elicit a systemic cytokine challenge and then measured pro-inflammatory gene expression in colonic mucosa. GC-C^+/+ and GC-C^−/− mice were bred with interleukin (IL)-10 deficient animals and colonic inflammation were assessed. Immune cell influx and cytokine/chemokine expression was measured in the colon of wildtype, IL-10^−/−, GC-C^+/+IL-10^−/− and GC-C^−/−IL-10^−/− mice. GC-C and guanylin production were examined in the colon of these animals and in a cytokine-treated colon epithelial cell line.

Results

Relative to GC-C^+/+ animals, intraperitoneal lipopolysaccharide injection into GC-C^−/− mice increased proinflammatory gene expression in both whole colon tissue and in partially purified colonocyte isolations. Spontaneous colitis in GC-C^−/−IL-10^−/− animals was significantly more severe relative to GC-C^+/+IL-10^−/− mice. Unlike GC-C^+/+IL-10^−/− controls, colon pathology in GC-C^−/−IL-10^−/− animals was apparent at an early age and was characterized by severely altered mucosal architecture, crypt abscesses, and hyperplastic subepithelial lesions. F4/80 and myeloperoxidase positive cells as well as proinflammatory gene expression were elevated in GC-C^−/−IL-10^−/− mucosa relative to control animals. Guanylin was diminished early in colitis in vivo and tumor necrosis factor α suppressed guanylin mRNA and protein in intestinal goblet cell-like HT29-18-N2 cells.

Conclusions

The GC-C signaling pathway blunts colonic mucosal inflammation that is initiated by systemic cytokine burst or loss of mucosal immune cell immunosuppression. These data as well as the apparent intestinal inflammation in human GC-C mutant kindred underscore the importance of GC-C in regulating the response to injury and inflammation within the gut.

Rodent intestinal epithelial carcinogenesis: pathology and preclinical models

Colon cancer is a major human malignancy that afflicts millions of people throughout the world each year. Genetics and diet play large roles in colon carcinogenesis although chemicals may also contribute. For the past 40 years, scientists have studied experimentally induced intestinal carcinogenesis in rodents in order to elucidate the etiology and mechanisms involved. Comparative histopathology has revealed many similarities of rodent and human intestinal cancers. Comparative molecular pathology has also shown genetic similarities. More recently, genetically engineered mice and inflammatory colon cancer models have been used for investigating mechanisms and potential chemopreventive and treatment modalities. This review will focus on comparative histopathology and nonclinical models.

Central role of the gut epithelial barrier in the pathogenesis of chronic intestinal inflammation: lessons learned from animal models and human genetics

The gut mucosa is constantly challenged by a bombardment of foreign antigens and environmental microorganisms. As such, the precise regulation of the intestinal barrier allows the maintenance of mucosal immune homeostasis and prevents the onset of uncontrolled inflammation. In support of this concept, emerging evidence points to defects in components of the epithelial barrier as etiologic factors in the pathogenesis of inflammatory bowel diseases (IBDs). In fact, the integrity of the intestinal barrier relies on different elements, including robust innate immune responses, epithelial paracellular permeability, epithelial cell integrity, as well as the production of mucus. The purpose of this review is to systematically evaluate how alterations in the aforementioned epithelial components can lead to the disruption of intestinal immune homeostasis, and subsequent inflammation. In this regard, the wealth of data from mouse models of intestinal inflammation and human genetics are pivotal in understanding pathogenic pathways, for example, that are initiated from the specific loss of function of a single protein leading to the onset of intestinal disease. On the other hand, several recently proposed therapeutic approaches to treat human IBD are targeted at enhancing different elements of gut barrier function, further supporting a primary role of the epithelium in the pathogenesis of chronic intestinal inflammation and emphasizing the importance of maintaining a healthy and effective intestinal barrier.

Mapping colitis susceptibility in mouse models: distal chromosome 3 contains major loci related to Cdcs1

Inflammatory bowel disease (IBD) summarizes a group of chronic intestinal disorders with Crohn's disease and ulcerative colitis being most prominent. Though much effort is put into identification of causative factors, its etiology is still not understood. Risk factors for disease development include genetic predisposition and environmental triggers. Crucial for identification and analysis of relevant factors are mouse models. Experimental IBD in mice occurs spontaneously or is induced by chemicals, cell transfer, pathogens, or genetic mutation. These models were utilized for analyzing genetic contribution to disease and genotype-environmental interactions. In these studies, a variety of modifier loci were identified, thereby demonstrating the complexity of disease. A major contribution of distal chromosome 3 was independently replicated in several studies. The first colitogenic QTL in this region was detected using the IL-10-deficient mouse model and called cytokine deficiency-induced colitis susceptibility (Cdcs)1. This quantitative trait locus contains at least three subintervals with independent genetic factors. This locus or defined subintervals were replicated in at least seven studies, using models based on dysregulation of innate or adaptive immunity or pathogen control. In this review we illustrate the various models used for genetic mapping of susceptibility to experimental IBD and display Cdcs1-related loci as well as the mechanism of their contribution identified so far.

Analysis of candidate colitis genes in the Gdac1 locus of mice deficient in glutathione peroxidase-1 and -2

Background

Mice that are deficient for glutathione peroxidases 1 and 2 (GPX) show large variations in the penetrance and severity of colitis in C57BL/6J and 129S1/SvImJ backgrounds. We mapped a locus contributing to this difference to distal chromosome 2 (∼119–133 mbp) and named it glutathione peroxidase-deficiency-associated colitis 1 (Gdac1). The aim of this study was to identify the best gene candidates within the Gdac1 locus contributing to the murine colitis phenotype.

Method/Principal Findings

We refined the boundaries of Gdac1 to 118–125 mbp (95% confidence interval) by increasing sample size and marker density across the interval. The narrowed region contains 128 well-annotated protein coding genes but it excludes Fermt1, a human inflammatory bowel disease candidate that was within the original boundaries of Gdac1. The locus we identified may be the Cdcs3 locus mapped by others studying IL10-knockout mice. Using in silico analysis of the 128 genes, based on published colon expression data, the relevance of pathways to colitis, gene mutations, presence of non-synonymous-single-nucleotide polymorphisms (nsSNPs) and whether the nsSNPs are predicted to have an impact on protein function or expression, we excluded 42 genes. Based on a similar analysis, twenty-five genes from the remaining 86 genes were analyzed for expression-quantitative-trait loci, and another 15 genes were excluded.

Conclusion/Significance

Among the remaining 10 genes, we identified Pla2g4f and Duox2 as the most likely colitis gene candidates, because GPX metabolizes PLA2G4F and DUOX2 products. Pla2g4f is a phospholipase A2 that has three potentially significant nsSNP variants and showed expression differences across mouse strains. PLA2G4F produces arachidonic acid, which is a substrate for lipoxygenases and, in turn, for GPXs. DUOX2 produces H₂O₂ and may control microbial populations. DUOX-1 and -2 control microbial populations in mammalian lung and in the gut of several insects and zebrafish. Dysbiosis is a phenotype that differentiates 129S1/SvImJ from C57BL/6J and may be due to strain differences in DUOX2 activity.

Mucosal healing and fibrosis after acute or chronic inflammation in wild type FVB-N mice and C57BL6 procollagen α1(I)-promoter-GFP reporter mice

Background

Injury and intestinal inflammation trigger wound healing responses that can restore mucosal architecture but if chronic, can promote intestinal fibrosis. Intestinal fibrosis is a major complication of Crohn’s disease. The cellular and molecular basis of mucosal healing and intestinal fibrosis are not well defined and better understanding requires well characterized mouse models.

Methods

FVB-N wild type mice and C57BL6 procollagen α1(I)-GFP reporter mice were given one (DSS1) or two (DSS2) cycles of 3% DSS (5 days/cycle) followed by 7 days recovery. Histological scoring of inflammation and fibrosis were performed at DSS1, DSS1+3, DSS1+7, DSS2, DSS2+3, and DSS2+7. Procollagen α1(I)-GFP activation was assessed in DSS and also TNBS models by whole colon GFP imaging and fluorescence microscopy. Colocalization of GFP with α-smooth muscle actin (α-SMA) or vimentin was examined. GFP mRNA levels were tested for correlation with endogenous collagen α1(I) mRNA.

Results

Males were more susceptible to DSS-induced disease and mortality than females. In FVB-N mice one DSS cycle induced transient mucosal inflammation and fibrosis that resolved by 7 days of recovery. Two DSS cycles induced transmural inflammation and fibrosis in a subset of FVB-N mice but overall, did not yield more consistent, severe or sustained fibrosis. In C57BL6 mice, procollagen α1(I)-GFP reporter was activated at the end of DSS1 and through DSS+7 with more dramatic and transmural activation at DSS2 through DSS2+7, and in TNBS treated mice. In DSS and TNBS models GFP reporter expression localized to vimentin⁺ cells and much fewer α-SMA⁺ cells. GFP mRNA strongly correlated with collagen α1(I) mRNA.

Conclusions

One DSS cycle in FVB-N mice provides a model to study mucosal injury and subsequent mucosal healing. The procollagen α1(I)-GFP transgenic provides a useful model to study activation of a gene encoding a major extracellular matrix protein during acute or chronic experimental intestinal inflammation and fibrosis.

Mouse background strain profoundly influences Paneth cell function and intestinal microbial composition

BACKGROUND

Increasing evidence supports the central role of Paneth cells in maintaining intestinal host-microbial homeostasis. However, the direct impact of host genotype on Paneth cell function remains unclear. Here, we characterize key differences in Paneth cell function and intestinal microbial composition in two widely utilized, genetically distinct mouse strains (C57BL/6 and 129/SvEv). In doing so, we demonstrate critical influences of host genotype on Paneth cell activity and the enteric microbiota.

METHODOLOGY AND PRINCIPAL FINDINGS

Paneth cell numbers were determined by flow cytometry. Antimicrobial peptide (AMP) expression was evaluated using quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR), acid urea-polyacrylamide gel electrophoresis, and mass spectrometry. Effects of mouse background on microbial composition were assessed by reciprocal colonization of germ-free mice from both background strains, followed by compositional analysis of resultant gut bacterial communities using terminal restriction fragment length polymorphism analysis and 16 S qPCR. Our results revealed that 129/SvEv mice possessed fewer Paneth cells and a divergent AMP profile relative to C57BL/6 counterparts. Novel 129/SvEv á-defensin peptides were identified, including Defa2/18v, Defa11, Defa16, and Defa18. Host genotype profoundly affected the global profile of the intestinal microbiota, while both source and host factors were found to influence specific bacterial groups. Interestingly, ileal α-defensins from 129/SvEv mice displayed attenuated antimicrobial activity against pro-inflammatory E. coli strains, a bacterial species found to be expanded in these animals.

CONCLUSIONS AND SIGNIFICANCE

This work establishes the important impact of host genotype on Paneth cell function and the composition of the intestinal microbiota. It further identifies specific AMP and microbial alterations in two commonly used inbred mouse strains that have varying susceptibilities to a variety of disorders, ranging from obesity to intestinal inflammation. This will be critical for future studies utilizing these murine backgrounds to study the effects of Paneth cells and the intestinal microbiota on host health and disease.

SAMP1/YitFc mouse strain: a spontaneous model of Crohn's disease-like ileitis

The SAMP1/YitFc mouse strain represents a model of Crohn's disease (CD)-like ileitis that is ideal for investigating the pathogenesis of chronic intestinal inflammation. Different from the vast majority of animal models of colitis, the ileal-specific phenotype characteristic of SAMP1/YitFc mice occurs spontaneously, without genetic, chemical, or immunological manipulation. In addition, SAMP1/YitFc mice possess remarkable similarities to the human condition with regard to disease location, histologic features, incidence of extraintestinal manifestations, and response to conventional therapies. SAMP1/YitFc mice also display a well-defined time course of a predisease state and phases of acute and chronic ileitis. As such, the SAMP1/YitFc model is particularly suitable for elucidating pathways that precede the clinical phenotype that may lead to preventive, and therefore more efficacious, intervention with the natural course of disease, or alternatively, for the development of therapeutic strategies directed against chronic, established ileitis. In this review we summarize important contributions made by our group and others that uncover potential mechanisms in the pathogenesis of CD using this unique murine model of chronic intestinal inflammation.

Quantitative trait loci in a bacterially induced model of inflammatory bowel disease

Inflammatory bowel diseases (IBDs) are complex disorders caused by a combination of environmental, microbial, and genetic factors. Genome-wide association studies in humans have successfully identified multiple genes and loci associated with disease susceptibility, but the mechanisms by which these loci interact with each other and/or with environmental factors (i.e., intestinal microbiota) to cause disease are poorly understood. Helicobacter hepaticus-induced intestinal inflammation in mice is an ideal model system for elucidating the genetic basis of IBD susceptibility in a bacterially induced system, as there are significant differences in H. hepaticus-induced disease susceptibility among inbred mouse strains. Infected A/J mice develop acute overexpression of proinflammatory cytokines followed 2-3 months later by chronic cecal inflammation, whereas infected C57BL/6 mice fail to develop cecal inflammation or increased cytokine expression. The goal of this project was to use quantitative trait locus (QTL) mapping to evaluate genetic factors that contribute to the differential disease susceptibility between these two mouse strains. Using acute cecal IL-12/23p40 expression as a biomarker for disease susceptibility, QTL analysis of H. hepaticus-infected F(2) mice revealed involvement of multiple loci. The loci with the strongest association were located on Chromosome 3 and Chromosome 17, with logarithm of odds (LOD) scores of 6.89 and 3.09, respectively. Cecal expression of IL-12/23p40 in H. hepaticus-infected C57BL/6J-Chr3(A/J)/NaJ chromosome substitution mice had an intermediate phenotype, significantly higher than in resistant C57BL/6 but lower than in susceptible A/J mice, confirming the importance of this locus to the immune response to H. hepaticus infection.

Colitis locus on chromosome 2 impacting the severity of early-onset disease in mice deficient in GPX1 and GPX2

BACKGROUND

Genetic background has a profound effect on inflammatory bowel disease. The Gpx1 and Gpx2 double knockout (GPX1/2-DKO) mice on a mixed C57BL/6 (B6) and 129S1/SvimJ (129) background exhibit spontaneous ileocolitis. The DKO mice on a B6 background have mild ileocolitis. We characterized the 129 DKO mice to identify a genetic locus affecting disease severity.

METHODS

We backcrossed B6;129 DKO mice to 129 and analyzed for ileocolitis penetrance and severity at N5, N7, and N10. By correlating disease severity with single-nucleotide polymorphism (SNP) markers, we identified a colitis locus.

RESULTS

As early as 9 days of age, 129 DKO N5 and N10 mice showed disease signs and morbidity. The N10 DKO mice had the severest colitis with nearly complete penetrance and high morbidity compared with other generations or backgrounds. 129 DKO mice had elevated colonic KC and SAA3 expression, shorter colon length, and cecal E. coli overgrowth compared to B6 DKO mice. Analysis of the B6 loci in 129 N5, N7, and N10 cohorts pointed to a region of chromosome 2: 119 Mbp contributing to mild symptoms.

CONCLUSIONS

GPX1/2-DKO mice on 129 genetic background have the most aggressive colitis compared to B6;129 and B6 colonies. A B6 locus significantly contributing the resistance resides on chromosome 2: 119 Mbp. This region coincides with cytokine-deficiency-induced colitis susceptibility, Cdcs3, identified in the resistant B6 and sensitive C3H/HeJBir (C3Bir) with IL-10 deficiency. A three-way SNP analysis between 129, B6, and C3Bir locus points the major candidate genes to B2m, Dnajc17, Duox2, Pla2g4b, Pla2g4e, Pla2g4f and Slc30a4.

Effects of appendectomy and oral tolerance on dextran sulfate sodium colitis

AIM: To evaluate the concomitant effects of appendectomy and oral tolerance on colitis.

METHODS: Delayed-type hypersensitivity (DTH) was investigated at a 7-d interval after ovalbumin (OVA) administration and immunization under normal and colitis conditions in appendectomized or sham-operated mice. Pathological scores for the colon were graded after ingestion of colon-extracted protein (CEP) and induction of dextran sulfate sodium (DSS) colitis in appendectomized or sham-operated mice. Thereafter, Th1 and Th2 in Peyer’s patches and spleen lymphocytes were detected in CEP-treated and bovine serum albumin (BSA)-treated control mice.

RESULTS: In appendectomized mice, DTH was not inhibited at day 7 after OVA administration and at the initial phase of DSS colitis, whereas it was inhibited at day 14 and day 21. However, in sham-operated mice, it was inhibited during the whole procedure and the onset of DSS colitis. The protective role of CEP against DSS colitis was present in sham-operated mice, with predominant improvement of colonic pathological changes, while vanished in the appendectomized mice. A shift from Th1 to Th2 in Peyer’s patches resulted from a decrease of Th1 cells with the ingestion of CEP. Compared with BSA in the sham-operated group, no predominant changes were observed in the appendectomized mice.

CONCLUSION: Appendectomy interferes with the protective role of CEP in DSS colitis via a shift from Th2 to Th1 during oral tolerance induction.

Gp91(phox) contributes to the development of experimental inflammatory bowel disease

Inflammatory bowel disease (IBD) is related to dysfunction of intestinal immunity. Neutrophils have an important role in innate immunity via the oxidative burst, using the p47phox- and gp91(phox)-containing NAD(P)H oxidase known as Nox2. In dextran sulphate sodium (DSS)-induced colitis, no significant difference in inflammation between p47(phox-/-) and wild-type (WT) mice was reported, but there was improved endothelium-dependent arteriolar dilation in gp91(phox-/-) mice, compared with that in WT mice. Gp91(phox) and p47 (phox) are not only essential components of phagocyte Nox2, but also have roles in other enzymes. Thus the differences in response of their respective gene knockout mice to DSS challenge are not completely unexpected, but need further investigation. The clinicopathological changes and immunological responses to DSS challenge have not been fully described in gp91(phox-/-) mice. Thus we treated WT and gp91(phox-/-) mice with 2.5% DSS for 7 days. The gp91(phox-/-) mice developed less severe colitis than WT mice following DSS treatment, reflected by a smaller body weight loss, less rectal bleeding and fewer histopathological changes. Less colonic myeloperoxidase was observed in gp91(phox-/-), compared with WT mice, following DSS challenge, correlating with interleukin (IL)-6 production. IL-10 was upregulated in both gp91(phox-/-) and WT mice, but was significantly higher in the latter, following 7 days DSS challenge. These results suggest that gp91(phox-/-) mice are less susceptible to acute DSS-induced colitis, possibly because of a reduced oxidative burst in the intestine and, consequently, less tissue damage.

Integrating mouse anatomy and pathology ontologies into a phenotyping database: tools for data capture and training

The Mouse Disease Information System (MoDIS) is a data capture system for pathology data from laboratory mice designed to support phenotyping studies. The system integrates the mouse anatomy (MA) and mouse pathology (MPATH) ontologies into a Microsoft Access database facilitating the coding of organ, tissue, and disease process to recognized semantic standards. Grading of disease severity provides scores for all lesions that can then be used for quantitative trait locus (QTL) analyses and haplotype association gene mapping. Direct linkage to the Pathbase online database provides reference definitions for disease terms and access to photomicrographic images of similar diagnoses in other mutant mice. MoDIS is an open source and freely available program (http://research.jax.org/faculty/sundberg/index.html). This provides a valuable tool for setting up a mouse pathology phenotyping program.

Mouse strain differences in inflammatory responses of colonic mucosa induced by dextran sulfate sodium cause differential susceptibility to PhIP-induced large bowel carcinogenesis

In mice, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) induces a high incidence of malignant lymphoma and leukemia, but exhibits little, if any, carcinogenic activity in the large intestine after long-term exposure. However, recent studies have revealed that colonic adenocarcinomas can be efficiently and rapidly induced by combined treatment with PhIP and dextran sulfate sodium (DSS), a potent inducer of colitis. In the present study, the authors investigated the effects of inflammation on PhIP-induced carcinogenesis using two mouse strains, C57BL/6J and MSM/Ms, showing distinct temporal profiles of inflammatory responses to DSS. A long-term carcinogenesis experiment conducted with a single i.g. administration of PhIP (200 mg/kg body weight), followed by DSS treatment in drinking water for 4-6 days, revealed an increase in tumor incidence in C57BL/6J mice in accordance with the DSS intake. In contrast, neoplastic lesions were rarely observed in the MSM/Ms strain. From the short-term exposure to DSS for 4 days, C57BL/6J mice demonstrated severe chronic colitis, accompanied by hyperplastic cryptal epithelium and extensive cellular infiltration. Splenomegaly and swelling of mesenteric lymph nodes were also evident for over 1 month as chronic symptoms of systemic immunological disturbance. However, no inflammatory lesions were detected in MSM/Ms mice. The present results provide strong evidence that prolonged chronic inflammatory responses induced by DSS are directly responsible for the observed enhancement of PhIP-induced large bowel carcinogenicity.

Cia25 on rat chromosome 12 regulates severity of autoimmune arthritis induced with pristane and with collagen

BACKGROUND

A genomewide scan in a DA x ACI F2 intercross studied for collagen-induced arthritis (CIA) identified the severity quantitative trait locus Cia25 on rat chromosome 12. Cia25 co-localises with loci regulating several forms of autoimmune diseases in rats, mice and humans, suggesting a common gene.

OBJECTIVE

To characterise the effects of Cia25 on severity of arthritis in congenic rats.

METHODS

DA.ACI(Cia25) congenic rats were constructed according to a genotype-guided strategy, and tested for pristane-induced arthritis (PIA) and CIA, induced with rat type II collagen (CII). A well-established scoring system previously shown to correlate with histological damage, including cartilage and bone erosions, synovial hyperplasia and synovial inflammation, was used.

RESULTS

The introgression of ACI alleles at Cia25 into DA background, as in DA.ACI(Cia25) rats, was enough to significantly reduce arthritis severity by 60% in PIA and by 40% in CIA, both in males and females compared with DA rats of the same sex. Levels of IgG anti-CII in male DA.ACI(Cia25) rats were 83% lower than in male DA. Levels of anti-CII in females were not affected by the congenic interval.

CONCLUSIONS

Cia25 contains a gene that regulates disease severity in two distinct models of autoimmune arthritis. Although both genders were protected in arthritis studies, only male congenic rats had a dramatic reduction in levels of anti-CII, suggesting the possibility of a second arthritis gene in this interval that operates via the regulation of autoantibodies in a sex-specific manner. The identification of the gene(s) accounting for Cia25 is expected to generate novel prognostic biomarkers and targets for therapy.

Molecular approaches to the role of the microbiota in inflammatory bowel disease

The microbiota plays a crucial role in experimental models of inflammatory bowel disease, but the exact mechanisms of its effects are unknown. These studies took two molecular approaches to this question. The first used amplification of the 16s ribosomal DNA to define microbial diversity in the colon. Although there were differences in colitic and non-colitic mice, we could not determine whether this was primary or secondary to the disease. The second approach used serologic expression cloning to identify the microbial proteins stimulating the pathogenic immune response. Previously unknown microbial flagellins were the dominant cluster of antigens identified. About half of the sera from patients with Crohn's disease have IgG antibodies to these flagellins.

Local production of chemokines and prostaglandin E2 in the acute, chronic and recovery phase of murine experimental colitis

Increased levels of chemokines and prostaglandins have been reported in patients with inflammatory bowel disease, although their changes during disease development are less understood. The aim of this study was to investigate the local production of nine selected chemokines and prostaglandin E(2) (PGE(2)) to elucidate their role in colitis progression in BALB/c and C57BL/6 mice exposed to dextran sulphate sodium. The acute inflammation in both strains was accompanied by a significant up-regulation of CXCL1, CXCL2/3, CXCL10, CCL2, CCL4 and CCL22 and a downregulation of PGE(2). In the recovery phase in BALB/c, one-week post-DSS, PGE(2) levels were significantly increased with a concomitant downregulation of CXCL1, CXCL2/3, CXCL10, CCL2, and CCL4. In contrast, in C57BL/6 mice CXCL1, CXCL2/3, CXCL10, CCL2, CCL3 and CCL4 production remained high during the chronic phase, without any up-regulation of PGE(2). In addition, CCL5 was significantly increased at d26 and 33 compared to d5. Interestingly, the number of macrophages was significantly increased during the acute phase, whereas T cells were significantly increased in both the acute and chronic phase in C57BL/6 mice. Thus, our results show that chemokines are produced in a dynamic manner during colitis progression.

Epithelial toll-like receptor 5 is constitutively localized in the mouse cecum and exhibits distinctive down-regulation during experimental colitis

We recently demonstrated that the pattern recognition receptors (PRRs) toll-like receptor 2 (TLR2), TLR4, and CD14 are expressed in mouse colonic epithelium in a compartmentalized manner. Here we report the localization of TLR5, the receptor for bacterial flagellin, and its distinctive down-regulation during experimental colitis. Guts from normal BALB/c mice and those with dextran sodium sulfate (DSS)-induced colitis were compared. Each gut was divided into seven segments (stomach, small intestine [three parts], and colon [three parts]), and epithelial cells and crypt units were collected by scraping and EDTA treatment, respectively. Northern blotting showed that TLR5 mRNA was preferentially expressed in the epithelium of the proximal colon in normal mice. Laser capture microdissection coupled to reverse transcriptase PCR confirmed this localization. TLR5 protein expression reflected mRNA expression, as evidenced by Western blotting. In mice with acute colitis, inflammation occurred mainly in the distal colon. Interestingly, while TLR2, TLR4, and CD14 were up-regulated in the inflamed colon, TLR5 was down-regulated at both the mRNA and protein levels. Decreased TLR5 expression was more evident during chronic colitis. Additional in vitro studies using a mouse cell line, Colon-26, showed that gamma interferon (IFN-gamma) time- and dose-dependently down-regulates TLR5. In conclusion, epithelial cells, mainly in the proximal colon, constitutively express TLR5. TLR5 expression is down-regulated in vivo during acute and chronic DSS-induced colitis, in contrast to the expression of TLR2, TLR4, and CD14. The mechanism governing TLR5 regulation may therefore differ from that controlling other PRRs. Finally, IFN-gamma may be involved in down-regulating TLR5 expression.

MUC genes are differently expressed during onset and maintenance of inflammation in dextran sodium sulfate-treated mice

Colonic mucosal protection is provided by mucous gel, mainly composed of secreted (Muc2) and membrane-bound (Muc1, Muc3, Muc4) mucins. Our aim was to determine the expression profile of secreted and membrane-bound mucins in experimental dextran sulfate sodium (DSS)-induced colitis. Acute colitis was induced in Balb/C mice by oral administration of 1.0% DSS (5 days) and chronic colitis was maintained by subsequent 0.15% DSS treatment (28 days). Clinical symptoms (mortality, weight gain), stool scores, and MPO activity confirmed the inflammatory state in the two phases of colitis. Muc2 gene expression was not modified by colitis, whereas Muc3 gene expression was increased (x2) only in the cecum and the distal colon of mice after acute colitis. Muc1 and Muc4 mRNA levels were more significantly increased in the cecum (x8-10) than in colonic segments (x4) after acute colitis. TFF3 involved in mucosal repair was up-regulated during colitis induction. These results indicate that Muc and TFF3 genes are regulated early in inflammation and suggest that their mRNA levels could be used as early markers of inflammation.

T helper 1-inducing property of IL-27/WSX-1 signaling is required for the induction of experimental colitis

BACKGROUND

WSX-1, a component of the interleukin (IL)-27 receptor, is a novel class I cytokine receptor with homology to the IL-12 receptor beta2 chain. Initially, WSX-1 signaling was reported to play an important role in the promotion of T helper-1 responses, but recent reports have revealed an anti-inflammatory property in WSX-1 signaling. In the present study, we investigated the role of IL-27/WSX-1 signaling in a murine colitis model, dextran sulfate sodium (DSS) colitis, by using WSX-1 knockout (KO) mice.

METHODS

First, we observed whether WSX-1 KO mice developed colitis spontaneously. Second, we induced DSS colitis in WSX-1 KO and wild-type (WT) mice.

RESULTS

WSX-1 KO mice were observed not to develop colitis spontaneously. The severity of DSS colitis was decreased in WSX-1 KO mice in comparison with WT mice in association with a reduced production of interferon-gamma, IL-6, and tumor necrosis factor-alpha by lamina propria mononuclear cells from WSX-1 KO mice and the absence of T-bet expression in the colon from WSX-1 KO mice.

CONCLUSIONS

This study revealed the inflammatory property of IL-27/WSX-1 signaling in intestinal inflammation. As a result, IL-27/WSX-1 signal pathway may thus be a promising candidate for the therapeutic intervention of human inflammatory bowel diseases such as Crohn's disease and ulcerative colitis.

Genetics of Crohn disease, an archetypal inflammatory barrier disease

Chronic inflammatory disorders such as Crohn disease, atopic eczema, asthma and psoriasis are triggered by hitherto unknown environmental factors that function on the background of some polygenic susceptibility. Recent technological advances have allowed us to unravel the genetic aetiology of these and other complex diseases. Using Crohn disease as an example, we show how the discovery of susceptibility genes furthers our understanding of the underlying disease mechanisms and how it will, ultimately, give rise to new therapeutic developments. The long-term goal of such endeavours is to develop targeted prophylactic strategies. These will probably target the molecular interaction on the mucosal surface between the products of the genome and the microbial metagenome of a patient.

Acute colitis induced by dextran sulfate sodium progresses to chronicity in C57BL/6 but not in BALB/c mice: correlation between symptoms and inflammation

Exposure to dextran sulfate sodium (DSS) induces acute colitis, which is normally resolved after DSS removal. To study chronicity, mice are typically subjected to three to five cycles of weekly DSS exposures, each followed by a 1- to 2-wk rest period. Here, we describe a novel and convenient way of inducing chronic, progressive colitis by a single exposure to DSS. C57BL/6 mice exposed to DSS for 5 days developed acute colitis that progressed to severe chronic inflammation. The plasma haptoglobin levels remained high during the chronic phase, showing that the inflammation was active. Surprisingly, the mice regained their original weight along with the progression of colitis, and the only apparent symptom was loose feces. Histopathological changes 4 wk after DSS removal were dense infiltrates of mononuclear cells, irregular epithelial structure, and persistent deposits of collagen. A progressive production of the cytokines IL-1beta, IL-12 p70, and IL-17 correlated with the extensive cellular infiltration, whereas high IFN-gamma production was mainly found late in the chronic phase. Similar to C57BL/6 mice, BALB/c mice exposed to 5 days of DSS developed acute colitis as previously described. The acute colitis was accompanied by elevated plasma levels of haptoglobin and increased colonic levels of IL-1alpha/beta, IL-6, IL-18, and granulocyte colony-stimulating factor. However, soon after DSS removal, BALB/c mice recovered and were symptom free within 2 wk and completely recovered 4 wk after DSS removal in terms of histopathology, haptoglobin levels, and local cytokine production. In summary, these data stress the effect of genetic background on the outcome of DSS provocation. We believe that the present protocol to induce chronic colitis in C57BL/6 mice offers a robust model for validating future therapies for treatment of inflammatory bowel disease.

A major quantitative trait locus on mouse chromosome 3 is involved in disease susceptibility in different colitis models

BACKGROUND & AIMS

Mice with a disrupted gene for the G-protein alpha inhibitory 2 chain ( Gnai2 -/- ) develop a spontaneous colitis resembling human inflammatory bowel disease. Disease expression differs markedly between inbred strains of mice, indicating genetic control of disease susceptibility. We performed a genome-wide screen to localize the chromosomal regions regulating disease expression.

METHODS

A total of 284 F2 mice derived from resistant C57BL/6J Gnai2 -/- mice and susceptible C3H/HeN Gnai2 -/- mice were analyzed in a genome-wide screen for colitis susceptibility and severity.

RESULTS

A highly significant locus on chromosome 3 (Gpdc1) contributed to colitis susceptibility and severity (likelihood ratio statistics [LRS] = 32.4; LOD score = 7; P < 1.0 x 10(-5)). The peak linkage of this locus at 62 cM colocalizes exactly with a previously identified locus controlling colitis susceptibility in interleukin-10-deficient mice. In addition, evidence for linkage with a locus on chromosome 1 (Gpdc2 ; LRS = 19.7; LOD = 4.3) was found, and the 2 loci interacted epistatically (combined LRS = 68.2). A third locus (Gpdc3) was found on chromosome 9 and this locus interacted epistatically with a locus on chromosome 7, which by itself did not have an effect on the trait.

CONCLUSIONS

The identification of a major locus on chromosome 3 that controls susceptibility to spontaneous colitis in 2 different gene-knockout models indicates that this locus harbors a gene(s) that plays a key role in maintaining mucosal homeostasis. Identification of this gene(s) may contribute to further understanding of the mechanisms underlying human inflammatory bowel disease.

Susceptibility to neoplastic and non-neoplastic pulmonary diseases in mice: genetic similarities

Chronic inflammation predisposes toward many types of cancer. Chronic bronchitis and asthma, for example, heighten the risk of lung cancer. Exactly which inflammatory mediators (e.g., oxidant species and growth factors) and lung wound repair processes (e.g., proangiogenic factors) enhance pulmonary neoplastic development is not clear. One approach to uncover the most relevant biochemical and physiological pathways is to identify genes underlying susceptibilities to inflammation and to cancer development at the same anatomic site. Mice develop lung adenocarcinomas similar in histology, molecular characteristics, and histogenesis to this most common human lung cancer subtype. Over two dozen loci, called Pas or pulmonary adenoma susceptibility, Par or pulmonary adenoma resistance, and Sluc or susceptibility to lung cancer genes, regulate differential lung tumor susceptibility among inbred mouse strains as assigned by QTL (quantitative trait locus) mapping. Chromosomal sites that determine responsiveness to proinflammatory pneumotoxicants such as ozone (O3), particulates, and hyperoxia have also been mapped in mice. For example, susceptibility QTLs have been identified on chromosomes 17 and 11 for O3-induced inflammation (Inf1, Inf2), O3-induced acute lung injury (Aliq3, Aliq1), and sulfate-associated particulates. Sites within the human and mouse genomes for asthma and COPD phenotypes have also been delineated. It is of great interest that several susceptibility loci for mouse lung neoplasia also contain susceptibility genes for toxicant-induced lung injury and inflammation and are homologous to several human asthma loci. These QTLs are described herein, candidate genes are suggested within these sites, and experimental evidence that inflammation enhances lung tumor development is provided.

Refined histopathologic scoring system improves power todetect colitis QTL in mice

Induction of colitis in mice by a targeted mutation in the I110 gene is inbred strain dependent. C3H/ HeJBir (C3H) mice are colitis susceptible while C57BL/6J (B6) mice are resistant. Identification of quantitative trait loci (QTL) determining the differential strain responsiveness requires histopathologic scoring of multiple lesion subphenotypes in both cecum and colon. Here we show that ability to detect a major C3H-derived QTL on Chr 3 (cytokine deficiency-induced colitis susceptibility 1, Cdcs1) was critically dependent upon the degree of refinement of the histopathologic scoring system. QTL mapping was performed using a first-back-cross population of interleukin-10-deficient mice and applying two different grading systems to assess lesion subphenotypes. The same histological specimens were scored by two independent pathologists using either a very detailed scoring system for four subphenotypes developed at The Jackson Laboratory (TJL) or a simpler scoring system developed at the Hannover Medical School (MHH). The more detailed TJL subphenotyping protocol increased power to identify Cdcs1 (a maximum LOD score of 4.28 versus a LOD score of 1.77 when using the abbreviated MHH subphenotyping scoring system). This study shows that for QTL mapping in a mouse model of colitis, in which histology represents the gold standard for phenotyping, ability to detect linkage is critically dependent upon the degree of refinement adopted for separately scoring the multiple histopathologic lesions comprising this complex phenotype.

Identification of two novel female-specific non-major histocompatibility complex loci regulating collagen-induced arthritis severity and chronicity, and evidence of epistasis

OBJECTIVE

To identify additional sex-specific and epistatic quantitative trait loci (QTL) regulating collagen-induced arthritis (CIA) severity overall, as well as within different stages during the disease course, in an intercross between major histocompatibility complex-identical inbred rat strains DA/Bkl (susceptible) and ACI/Hsd (resistant).

METHODS

Arthritic male (DA x ACI)F2 intercross offspring (n = 143) were analyzed separately from the females (n = 184). Phenotypic extremes (maximum arthritis scores [MAS]) were genotyped and used for QTL analysis. All 327 rats were genotyped with the simple sequence-length polymorphism (SSLP) markers closest to the peak of Cia7 and Cia10, the major loci previously identified in this intercross, and with SSLPs covering chromosomes 12 and 18. Phenotypes studied were disease onset, arthritis severity scores on days 14-39, MAS, mean and cumulative arthritis scores, delayed-type hypersensitivity, and antibody responses to rat type II collagen.

RESULTS

A new female-specific arthritis-severity recessive locus was identified on rat chromosome 12 (Cia25), with a maximum effect observed on day 28 (logarithm of odds [LOD] 4.7). The homozygous DA genotype at Cia25 was associated with a 45% higher median arthritis score in females. Sequencing analyses of the Cia25 candidate gene Ncf1 revealed polymorphisms between DA and ACI. The previously identified locus, Cia10, was found to be male-specific. A 2-locus interaction model analysis identified a novel recessive chromosome 18 QTL, Cia26, which was dependent on Cia7, with its maximum effect observed at later stages during the disease course (peak LOD score of 3.6 for arthritis scores on day 39).

CONCLUSION

This study identified 2 novel female-specific loci, and 1 male-specific locus. Cia25 regulates MAS and disease severity during the mid-to-late stages of the disease course and may be accounted for by Ncf1 polymorphisms. Cia26 is in epistasis with Cia7 and regulates later stages of disease, suggesting an involvement in disease perpetuation and/or chronicity.

Identification of a quantitative trait locus for ileitis in a spontaneous mouse model of Crohn's disease: SAMP1/YitFc

BACKGROUND & AIMS

The SAMP1/Yit mouse strain develops spontaneous ileitis with histologic features of Crohn's disease. Disease expression in the SAMP1/YitFc subline (SAMP1/Fc) is partially inhibited by outcross to C57BL/6J (B6) mice, suggesting complex genetic control of disease susceptibility with both dominant and recessive determinants. We performed a genetic analysis of a (B6 x SAMP1/Fc)F(2) cross to localize the genes regulating intestinal inflammation in this model.

METHODS

A genome-wide scan was performed using a panel of microsatellite loci determined to be informative for this cross. Quantitative trait loci were identified with Map Manager QT using a serial regression approach. Positional candidate genes were selectively sequenced at the genomic level to identify potential susceptibility genes for functional screening.

RESULTS

A genome-wide scan of (B6 x SAMP1/Fc)F(2) mice identified a SAMP-derived quantitative trait loci with additive effects on chromosome 9 in a region likely to have been inherited from the AKR mouse strain. The candidate interval contains several genes of interest because of their potential role in either immune system function, intestinal epithelial function, or both. Suggestive evidence for additional loci was also observed on chromosomes 6 and X.

CONCLUSIONS

The SAMP1/Fc allele for a locus, designated Ibdq1, promotes inflammation-associated epithelial damage in these mice. Consistent with persistent mild ileitis in (B6 x SAMP1/Fc)F(1) mice, this locus appears to function in an additive fashion. Two genes in this interval, encoding the interleukin 10 receptor alpha chain and interleukin 18, are excellent candidates for Ibdq1.

The immunological and genetic basis of inflammatory bowel disease

The inflammatory bowel diseases (IBDs), Crohn's disease and ulcerative colitis, are chronic inflammatory disorders of the gastrointestinal tract. Enormous progress has been made recently in understanding the pathogenesis of these diseases. Through the study of patients and mouse models, it has emerged that Crohn's disease is driven by the production of interleukin-12 (IL-12) and interferon-gamma (IFN-gamma), whereas ulcerative colitis is probably driven by the production of IL-13. A second area of progress is in the identification of specific genetic abnormalities that are responsible for disease. The most important finding is the identification of mutations in the gene that encodes NOD2 (nucleotide-binding oligomerization domain 2) protein in a subgroup of patients with Crohn's disease. Here, we discuss these recent findings and the implications for therapy.

Major locus on mouse chromosome 17 and minor locus on chromosome 9 are linked with alopecia areata in C3H/HeJ mice

Alopecia areata is an autoimmune disease that targets actively growing (anagen) hair follicles in humans, mice, rats, dogs, horses, and cattle. C3H/HeJ mice spontaneously develop alopecia areata from 5 mo of age and older in females and later in males. Frequency of disease approached 20% in a colony by 18 mo of age. C57BL/6J mice do not develop alopecia areata. A segregating F2 population of female mice (n=1096) was generated from crossing these two strains. Alopecia areata (n=138) and clinically normal (n=214) mice were genotyped at 12 mo of age using 211 microsatellite probes. The peak logarithm of odds ratio score on mouse chromosome 17 (10.9) was around marker D17Mit134 at 16.9 cM from the centromere. The mouse histocompatibility locus, H2, the mouse equivalent of human leukocyte antigen in humans, was a likely candidate. Twelve-month-old C3H.SW-H2b/SnJ mice (C3H/HeJ congenic mice in which the H2k purported susceptibility locus was replaced with the H2b purported resistance locus) did not develop alopecia areata, supporting this locus as being important in alopecia areata. A suggestive linkage was also found on mouse Chromosome 9 (logarithm of odds ratio score 2.0) around D9Mit206, 20 cM from the centromere. The interval on mouse Chromosome 17 contains several orthologous genes potentially associated with human alopecia areata.

Rapid development of colitis in NSAID-treated IL-10-deficient mice

BACKGROUND & AIMS

Interleukin (IL)-10 is an anti-inflammatory and immune regulatory cytokine. IL-10-deficient mice (IL-10(-/-)) develop chronic inflammatory bowel disease (IBD), indicating that endogenous IL-10 is a central regulator of the mucosal immune response. Prostaglandins are lipid mediators that may be important mediators of intestinal inflammation. In this study we assessed the role of prostaglandins in the regulation of mucosal inflammation in the IL-10(-/-) mouse model of IBD.

METHODS

Prostaglandin (PG) synthesis was inhibited with nonselective or cyclooxygenase (COX)-isoform selective inhibitors. Severity of inflammation was assessed histologically. Cytokine production was assessed by ribonuclease protection analysis and enzyme-linked immunosorbent assay. PGE(2) levels were assessed by enzyme immunoassay. COX-1 and COX-2 expression was assessed by Western blot analysis.

RESULTS

Nonsteroidal anti-inflammatory drug (NSAID) treatment of wild-type mice had minimal effect on the colon. In contrast, NSAID treatment of 4-week-old IL-10(-/-) mice resulted in rapid development of colitis characterized by infiltration of the lamina propria with macrophages and interferon gamma-producing CD4(+) T cells. Colitis persisted after withdrawal of the NSAID. NSAID treatment decreased colonic PGE(2) levels by 75%. Treatment of IL-10(-/-) mice with sulindac sulfone (which does not inhibit PG production) did not induce colitis whereas the NSAID sulindac induced severe colitis. COX-1- or COX-2-selective inhibitors used alone did not induce IBD in IL-10(-/-) mice. However, the combination of COX-1- and COX-2-selective inhibitors did induce colitis.

CONCLUSIONS

NSAID treatment of IL-10(-/-) mice results in the rapid development of severe, chronic IBD. Endogenous PGs are important inhibitors of the development of intestinal inflammation in IL-10(-/-) mice.

Genetic and environmental context determines the course of colitis developing in IL-10-deficient mice

This review summarizes how interleukin-10 (IL-10)-deficient mice have permitted new insight into the complex interaction between genes and environment underlying pathogenesis of inflammatory bowel disease (IBD). The C57BL/6J strain develops only mild typhlocolitis in response to IL-10 deficiency. In contrast, C3H/HeJBir represents an unrelated inbred strain with high IBD susceptibility. Ability to identify quantitative trait loci segregating for susceptibility when the two IL-10-deficient stocks were intercrossed depended both on genome "context" (F2 versus reciprocal backcrosses) and on the physical environment. These findings are discussed in the context of recent advances in understanding the complex genetic basis for IBD in humans.

Genetic susceptibility to chronic periodontal disease

Evidence suggests that there is a significant genetic component to susceptibility and resistance to chronic periodontal disease. Data from both clinical studies and studies using animal models are reviewed here. Also outlined are the genomic methods that are now available for identifying susceptibility and resistance loci.

Genetics of colitis susceptibility in IL-10-deficient mice: backcross versus F2 results contrasted by principal component analysis

Interleukin-10-deficient (Il10(-/-)) mice on a C3H/HeJBir genetic background develop more severe colitis than those on a C57BL/6J background. We performed genome screens for quantitative trait loci (QTLs) regulating colitis susceptibility in this model system using two first backcross populations derived from these two strains. To reduce the complexity of this analysis, the information from numerous histologic phenotypes was summarized by principal component analysis. A similar approach was applied to previously published data from an F2 intercross (involving the same progenitor strains), which allowed us to ascertain all six previously reported cytokine-deficiency-induced colitis susceptibility loci (Cdcs1-6) with main and/or interacting effects on chromosomes 3, 1, 2, 8, 17, and 18. The colitogenic effect of Cdcs1 was confirmed in the backcross to C3H/HeJBir-Il10(-/-). Its effect was epistatically modified by another locus on chromosome 12. In addition, three main effect QTLs on chromosomes 4, 5, and 12 were identified in the backcross to C57BL/6J-Il10(-/-). Analyses of the modes of inheritance in these crosses revealed colitogenic contributions by both parental genomes. These findings show the complexity of inheritance underlying susceptibility to colitis and illustrate why detection of human inflammatory bowel disease loci has proven to be so difficult.

Experimental murine colitis is regulated by two genetic loci, including one on chromosome 11 that regulates IL-12 responses

BACKGROUND & AIMS

Immunogenetic analysis of experimental colitis may contribute to the further unraveling of the complex genetic basis of the inflammatory bowel diseases, Crohn's disease and ulcerative colitis.

METHODS

Genetic regions associated with susceptibility to trinitrobenzene sulfonic acid (TNBS)-induced colitis were identified in a genome-wide linkage analysis in F2 progeny of colitis-susceptible SJL/J and -resistant C57BL/6 mice. An immunogenetic approach was then used to further study the pathophysiologic role of one of the identified loci.

RESULTS

We identified susceptibility loci on chromosomes 9 (Tnbs1) and 11 (Tnbs2). Tnbs2 harbors the interleukin (IL)-12 p40 gene, a likely candidate gene because IL-12 is a known central mediator for both experimental colitis and human Crohn's disease. We therefore tested the ability of colitis-susceptible and -resistant strains to mount IL-12 responses to lipopolysaccharide (LPS), a strong inducer of IL-12 that is abundantly present in the intestine. We observed a remarkably higher serum IL-12 response to LPS in susceptible SJL/J mice. Subsequently, we showed that the genetic region regulating the IL-12 response to LPS colocalizes with Tnbs2.

CONCLUSIONS

These data strongly suggest that the tendency to mount a high LPS-induced IL-12 response and susceptibility to TNBS-induced colitis are related and that in fact a genetically determined high IL-12 response is involved in the immunologic basis of susceptibility to colitis.

The immunology of mucosal models of inflammation

In recent years the status of the inflammatory bowel diseases (IBDs) as canonical autoimmune diseases has risen steadily with the recognition that these diseases are, at their crux, abnormalities in mucosal responses to normally harmless antigens in the mucosal microflora and therefore responses to antigens that by their proximity and persistence are equivalent to self-antigens. This new paradigm is in no small measure traceable to the advent of multiple models of mucosal inflammation whose very existence is indicative of the fact that many types of immune imbalance can lead to loss of tolerance for mucosal antigens and thus inflammation centered in the gastrointestinal tract. We analyze the immunology of the IBDs through the lens of the murine models, first by drawing attention to their common features and then by considering individual models at a level of detail necessary to reveal their individual capacities to provide insight into IBD pathogenesis. What emerges is that murine models of mucosal inflammation have given us a road map that allows us to begin to define the immunology of the IBDs in all its complexity and to find unexpected ways to treat these diseases.

The genetics of inflammatory bowel disease

The complex genetics of IBD is characterized by more than one susceptibility locus, genetic heterogeneity, incomplete penetrance, and probable gene-gene and gene-environment interactions. Functional candidate gene association studies during the past few decades have revealed only modest associations between IBD and genetic variants in the HLA genes and a limited number of other genes that are involved in immune regulation and the inflammatory response. Important advances in IBD genetics research have come about from systematic genome searches for IBD loci. The identification of Crohn's disease-associated NOD2 genetic variants that appear to alter the innate immune response to bacteria is a seminal finding that perhaps is the greatest advance toward understanding the pathogenesis of IBD in decades. The future discovery of other IBD genetic risk factors, facilitated by the completion of the human genome sequencing and annotation, may allow the development of better therapies, possibly including preventive therapies, for patients with Crohn's disease and ulcerative colitis.