The gastrointestinal microbiome: a malleable, third genome of mammals

The nonpathogenic, mutualistic bacteria of the mammalian gastrointestinal tract provide a number of benefits to the host. Recent reports have shown how the aggregate genomes of gastrointestinal bacteria provide novel benefits by functioning as the third major genome in mammals along with the nuclear and mitochondrial genomes. Consequently, efforts are underway to elucidate the complexity of the organisms comprising the unique ecosystem of the gastrointestinal tract, as well as those associated with other epidermal surfaces. The current knowledge of the gastrointestinal microbiome, its relationship to human health and disease with a particular focus on mammalian physiology, and efforts to alter its composition as a novel therapeutic approach are reviewed

Murine models of colorectal cancer

Colorectal cancer is one of the most prevalent cancers of humans. To experimentally investigate this common disease, numerous murine models have been established. These models accurately recapitulate the molecular and pathological characteristics of human colorectal cancer including activation of MYC, which has recently been suggested to be a key mediator of colorectal cancer development. This review focuses on the variety of murine models of human colorectal cancer that are available to the research community and on their use to identify common and distinct characteristics of colorectal cancer

Wildtype epidermal growth factor receptor (Egfr) is not required for daily locomotor or masking behavior in mice

BACKGROUND: Recent studies have implicated the epidermal growth factor receptor (EGFR) within the subparaventricular zone as being a major mediator of locomotor and masking behaviors in mice. The results were based on small cohorts of mice homozygous for the hypomorphic Egfr(wa2 )allele on a mixed, genetically uncontrolled background, and on intraventricular infusion of exogenous EGFR ligands. Subsequenlty, a larger study using the same genetically mixed background failed to replicate the original findings. Since both previous approaches were susceptible to experimental artifacts related to an uncontrolled genetic background, we analyzed the locomotor behaviors in Egfr(wa2 )mutant mice on genetically defined, congenic backgrounds. METHODS: Mice carrying the Egfr(wa2 )hypomorphic allele were bred to congenicity by backcrossing greater than ten generations onto C57BL/6J and 129S1/SvImJ genetic backgrounds. Homozygous Egfr(wa2 )mutant and wildtype littermates were evaluated for defects in locomotor and masking behaviors. RESULTS: Mice homozygous for Egfr(wa2 )showed normal daily locomotor activity and masking indistinguishable from wildtype littermates at two light intensities (200–300 lux and 400–500 lux). CONCLUSION: Our results demonstrate that reduced EGFR activity alone is insufficient to perturb locomotor and masking behaviors in mice. Our results also suggest that other uncontrolled genetic or environmental parameters confounded previous experiments linking EGFR activity to daily locomotor activity and provide a cautionary tale for genetically uncontrolled studies

Dietary calcium supplementation enhances efficacy but also toxicity of EGFR inhibitor therapy for colon cancer

The inverse correlation between levels of dietary calcium and colorectal cancer (CRC) incidence has been extensively investigated. However, the impact of supplemental calcium on cancer therapy remains unknown. We used four models of CRC, Caco-2 and HCT116 human cancer cell lines and ApcMin/+ and azoxymethane carcinogen-induced mouse models, to investigate the impact of a Western-style diet low in calcium (0.05%) vs. a similar diet but supplemented with calcium (5%) on therapeutic targeting of the epidermal growth factor receptor (EGFR). We found that calcium supplementation combined with pharmacologic blockade of EGFR results in an additive effect on tumor growth inhibition in all models. Unexpectedly, the combined use of dietary calcium supplementation and EGFR inhibitors also resulted in elevated toxicity suggesting that careful consideration be given when combining dietary supplements with prescribed cancer therapies

Modulation of Colorectal Cancer by the Probiotic Organism Lactobacillus Reuteri

Abstract Probiotics are beneficial to gastrointestinal health and have anti-inflammatory properties. An experiment was conducted to determine if L. reuteri could protect mice from azoxymethane-induced colorectal cancer (AOM-CRC). A/J mice were randomly assigned to controls, pre-treatment, or post-treatment groups. The mice in the groups were injected with 10mg/kg body weight of AOM and treated with L. reuteri; given only AOM; given only L. reuteri; or given neither AOM nor L. reuteri. At the end of a 26-week latency period, the mice were euthanized, dissected, and colons examined for tumors. L. reuteri did not protect animals against tumor formation. However, L. reuteri treatment had a significant effect on tumor number when the mice were segregated by gender (p = 0.014). There was no significant effect of regimen on tumor number (p = 0.667) or tumor size (p = 0.197). Ultimately, L. reuteri exhibited probiotic properties as a potential prophylactic treatment for colitis

Genetic mapping and developmental timing of transmission ratio distortion in a mouse interspecific backcross

<p>Abstract</p> <p>Background</p> <p>Transmission ratio distortion (TRD), defined as statistically significant deviation from expected 1:1 Mendelian ratios of allele inheritance, results in a reduction of the expected progeny of a given genotype. Since TRD is a common occurrence within interspecific crosses, a mouse interspecific backcross was used to genetically map regions showing TRD, and a developmental analysis was performed to identify the timing of allele loss.</p> <p>Results</p> <p>Three independent events of statistically significant deviation from the expected 50:50 Mendelian inheritance ratios were observed in an interspecific backcross between the <it>Mus musculus </it>A/J and the <it>Mus spretus </it>SPRET/EiJ inbred strains. At weaning <it>M. musculus </it>alleles are preferentially inherited on Chromosome (Chr) 7, while <it>M. spretus </it>alleles are preferentially inherited on Chrs 10 and 11. Furthermore, alleles on Chr 3 modify the TRD on Chr 11. All TRD loci detected at weaning were present in Mendelian ratios at mid-gestation and at birth.</p> <p>Conclusions</p> <p>Given that Mendelian ratios of inheritance are observed for Chr 7, 10 and 11 during development and at birth, the underlying causes for the interspecific TRD events are the differential post-natal survival of pups with specific genotypes. These results are consistent with the TRD mechanism being deviation from Mendelian inheritance rather than meiotic drive or segregation distortion.</p

Mapping Six New Susceptibility to Colon Cancer ( Scc ) Loci Using a Mouse Interspecific Backcross

Colorectal cancer (CRC) has a complex etiology resulting from the combination of multiple genetic and environmental factors, each with small effects. Interactions among susceptibility modifier loci make many of the loci difficult to detect in human genome-wide association studies. Previous analyses in mice have used classical inbred strains, which share large portions of their genomes due to common ancestry. Herein, we used an interspecific backcross between the Mus musculus strain A/J and the Mus spretus strain SPRET/EiJ to map 6 additional CRC modifier loci (Scc16-21) and 2 suggestive loci. Three loci modify the location of tumors along the proximal-distal axis of the colon. Six CRC modifiers previously mapped in intraspecific crosses were also replicated. This work confirms genetic models suggesting that CRC is caused by many small effect alleles and brings the catalog of reported CRC modifier loci to 23 spread across 13 chromosomes. Furthermore, this work provides the foundation for large population-level epistatic interaction tests to identify combinations of low effect alleles that may have large effects on CRC susceptibility

Chronic pharmacologic inhibition of EGFR leads to cardiac dysfunction in C57BL/6J mice

Molecule-targeted therapies like those against the epidermal growth factor receptor (EGFR) are becoming widely used in the oncology clinic. With improvements in treatment efficacy, many cancers are being treated as chronic diseases, with patients having prolonged exposure to several therapies that were previously only given acutely. The consequence of chronic suppression of EGFR activity may lead to unexpected toxicities like altered cardiac physiology, a common organ site for adverse drug effects. To explore this possibility, we treated C57BL/6J (B6) mice with two EGFR small molecule tyrosine kinase inhibitors (TKIs), irreversible EKB-569 and reversible AG-1478, orally for three months. In B6 female mice, chronic exposure to both TKIs depressed body weight gain and caused significant changes in left ventricular (LV) wall thickness and cardiac function. No significant differences were observed in heart weight or cardiomyocyte size but histological analysis revealed an increase in fibrosis and in the numbers of TUNEL-positive cells in the hearts from treated female mice. Consistent with histological results, LV apoptotic gene expression was altered, with significant downregulation of the anti-apoptotic gene Bcl2l1. Although there were no significant differences in any of these endpoints in treated male mice, suggesting sex may influence susceptibility to TKI mediated toxicity, the LVs of treated male mice had significant upregulation of Egf, Erbb2 and Nppb over controls. Taken together, these data suggest that chronic dietary exposure to TKIs may result in pathological and physiological changes in the heart

Toxicogenetics: population-based testing of drug and chemical safety in mouse models

The rapid decline in the cost of dense genotyping is paving the way for new DNA sequence-based laboratory tests to move quickly into clinical practice, and to ultimately help realize the promise of ‘personalized’ therapies. These advances are based on the growing appreciation of genetics as an important dimension in science and the practice of investigative pharmacology and toxicology. On the clinical side, both the regulators and the pharmaceutical industry hope that the early identification of individuals prone to adverse drug effects will keep advantageous medicines on the market for the benefit of the vast majority of prospective patients. On the environmental health protection side, there is a clear need for better science to define the range and causes of susceptibility to adverse effects of chemicals in the population, so that the appropriate regulatory limits are established. In both cases, most of the research effort is focused on genome-wide association studies in humans where de novo genotyping of each subject is required. At the same time, the power of population-based preclinical safety testing in rodent models (e.g., mouse) remains to be fully exploited. Here, we highlight the approaches available to utilize the knowledge of DNA sequence and genetic diversity of the mouse as a species in mechanistic toxicology research. We posit that appropriate genetically defined mouse models may be combined with the limited data from human studies to not only discover the genetic determinants of susceptibility, but to also understand the molecular underpinnings of toxicity

Dietary Fat Alters Body Composition, Mammary Development, and Cytochrome P450 Induction after Maternal TCDD Exposure in DBA/2J Mice with Low-Responsive Aryl Hydrocarbon Receptors

BackgroundIncreased fat intake is associated with obesity and may make obese individuals uniquely susceptible to the effects of lipophilic aryl hydrocarbon receptor (AHR) ligands.ObjectivesWe investigated the consequences of high-fat diet (HFD) and AHR ligands on body composition, mammary development, and hepatic P450 expression.MethodsPregnant C57BL/6J (B6) and DBA/2J (D2) dams, respectively expressing high- or low-responsive AHR, were dosed at mid-gestation with TCDD. At parturition, mice were placed on an HFD or a low-fat diet (LFD). Body fat of progeny was measured before dosing with 7,12-dimethylbenz[a]anthracene (DMBA). Fasting blood glucose was measured, and liver and mammary glands were analyzed.ResultsMaternal TCDD exposure resulted in reduced litter size in D2 mice and, on HFD, reduced postpartum survival in B6 mice. In D2 mice, HFD increased body mass and fat in off-spring, induced precocious mammary gland development, and increased AHR expression compared with mice given an LFD. Maternal TCDD exposure increased hepatic Cyp1a1 and Cyp1b1 expression in offspring on both diets, but DMBA depressed Cyp1b1 expression only in mice fed an HFD. In D2 progeny, TCDD exposure decreased mammary terminal end bud size, and DMBA exposure decreased the number of terminal end buds. Only in D2 progeny fed HFD did perinatal TCDD increase blood glucose and the size of mammary fat pads, while decreasing both branch elongation and the number of terminal end buds.ConclusionsWe conclude that despite having a low-responsive AHR, D2 progeny fed a diet similar to that consumed by most people are susceptible to TCDD and DMBA exposure effects blood glucose levels, mammary differentiation, and hepatic Cyp1 expression