Genetics of liver tumor susceptibility in mice

Both Maternal High-Fat and Post-Weaning High-Carbohydrate Diets Increase Rates of Spontaneous Hepatocellular Carcinoma in Aged-Mouse Offspring

Both maternal obesity and postnatal consumption of obesogenic diets contribute to the development of metabolic dysfunction-associated steatotic liver disease (MASLD) and hepatocellular carcinoma (HCC). However, there is no consensus as to whether diets that are high in fat or carbohydrates/sugars differentially influence the development of HCC. Moreover, the long-term effects of prenatal HF exposure on HCC and whether this is influenced by postnatal diet has not yet been evaluated. C57BL/6 dams were fed either a low-fat, high-carbohydrate control (C) or low-carbohydrate, high-fat (HF) diet. At weaning, male and female offspring were fed the C or HF diet, generating four diet groups: C/C, C/HF, HF/C and HF/HF. Tissues were collected at 16 months of age and livers were assessed for MASLD and HCC. Glucose regulation and pancreatic morphology were also evaluated. Liver tissues were assessed for markers of glycolysis and fatty acid metabolism and validated using a human HCC bioinformatic database. Both C/HF and HF/HF mice developed obesity, hyperinsulinemia and a greater degree of MASLD than C/C and HF/C offspring. However, despite significant liver and pancreas pathology, C/HF mice had the lowest incidence of HCC while tumour burden was highest in HF/C male offspring. The molecular profile of HCC mouse samples suggested an upregulation of the pentose phosphate pathway and a downregulation of fatty acid synthesis and oxidation, which was largely validated in the human dataset. Both pre-weaning HF diet exposure and post-weaning consumption of a high-carbohydrate diet increased the risk of developing spontaneous HCC in aged mice. However, the influence of pre-weaning HF feeding on HCC development appeared to be stronger in the context of post-weaning obesity. As rates of maternal obesity continue to rise, this has implications for the future incidence of HCC and possible dietary manipulation of offspring carbohydrate intake to counteract this risk.

Impact of Cyanotoxin Ingestion on Liver Cancer Development Using an At-Risk Two-Staged Model of Mouse Hepatocarcinogenesis

Exposure to cyanobacterial hepatotoxins has been linked to the promotion and increased incidence of liver cancer in pre-clinical and epidemiologic studies. The family of hepatotoxins, microcystins (MCs), are produced by over 40 cyanobacterial species found in harmful algal blooms (HABs) worldwide, with MC-LR being the most common and potent MC congener. In the current study, we hypothesized that the low-dose chronic ingestion of Microcystis cyanotoxins via drinking water would promote liver carcinogenesis in pre-initiated mice. Four groups of C3H/HeJ mice received one intraperitoneal (i.p.) injection of diethylnitrosamine (DEN) at 4 weeks of age. Three weeks later, the mice were administered ad libitum drinking water containing one of the following: (1) reverse osmosis, deionized water; (2) water containing 500 mg/L phenobarbital (PB500); (3) water with purified MC-LR (10 µg/L) added; or (4) water containing lysed Microcystis aeruginosa (lysate; 10 µg/L total MCs). The exposure concentrations were based on environmentally relevant concentrations and previously established Ohio EPA recreational water MC guidelines. Throughout the 30-week exposure, mouse weights, food consumption, and water consumption were not significantly impacted by toxin ingestion. We found no significant differences in the number of gross and histopathologic liver lesion counts across the treatment groups, but we did note that the PB500 group developed lesion densities too numerous to count. Additionally, the proportion of lesions classified as hepatocellular carcinomas in the MC-LR group (44.5%; p < 0.05) and lysate group (55%; p < 0.01) was significantly higher compared to the control group (14.9%). Over the course of the study, the mice ingesting the lysate also had a significantly lower survival probability (64.4%; p < 0.001) compared to water (96.8%), PB500 (95.0%), and MC-LR (95.7%) exposures. Using cyanotoxin levels at common recreational water concentration levels, we demonstrate the cancer-promoting effects of a single cyanotoxin MC congener (MC-LR). Furthermore, we show enhanced hepatocarcinogenesis and significant mortality associated with combinatorial exposure to the multiple MCs and bioactive compounds present in lysed cyanobacterial cells—a scenario representative of the ingestion exposure route, such as HAB-contaminated water and food.

In Vivo and In Vitro Models of Hepatocellular Carcinoma: Current Strategies for Translational Modeling

Hepatocellular carcinoma (HCC) is the sixth most common cancer worldwide and the third leading cause of cancer-related death globally. HCC is a complex multistep disease and usually emerges in the setting of chronic liver diseases. The molecular pathogenesis of HCC varies according to the etiology, mainly caused by chronic hepatitis B and C virus infections, chronic alcohol consumption, aflatoxin-contaminated food, and non-alcoholic fatty liver disease associated with metabolic syndrome or diabetes mellitus. The establishment of HCC models has become essential for both basic and translational research to improve our understanding of the pathophysiology and unravel new molecular drivers of this disease. The ideal model should recapitulate key events observed during hepatocarcinogenesis and HCC progression in view of establishing effective diagnostic and therapeutic strategies to be translated into clinical practice. Despite considerable efforts currently devoted to liver cancer research, only a few anti-HCC drugs are available, and patient prognosis and survival are still poor. The present paper provides a state-of-the-art overview of in vivo and in vitro models used for translational modeling of HCC with a specific focus on their key molecular hallmarks.

Tumor aggressiveness is independent of radiation quality in murine hepatocellular carcinoma and mammary tumor models

PURPOSE

Estimating cancer risk associated with interplanetary space travel is complicated. Human exposure data to high atomic number, high-energy (HZE) radiation is lacking, so data from low linear energy transfer (low-LET) γ-ray radiation is used in risk models, with the assumption that HZE and γ-ray radiation have comparable biological effects. This assumption has been challenged by reports indicating that HZE radiation might produce more aggressive tumors. The goal of this research is to test whether high-LET HZE radiation induced tumors are more aggressive.

MATERIALS AND METHODS

Murine models of mammary and liver cancer were used to compare the impact of exposure to 0.2Gy of 300MeV/n silicon ions, 3 Gy of γ-rays or no radiation. Numerous measures of tumor aggressiveness were assessed.

RESULTS

For the mammary cancer models, there was no significant change in the tumor latency or metastasis in silicon-irradiated mice compared to controls. For the liver cancer models, we observed an increase in tumor incidence but not tumor aggressiveness in irradiated mice.

CONCLUSION

Tumors in the HZE-irradiated mice were not more aggressive than those arising from exposure to low-LET γ-rays or spontaneously. Thus, enhanced aggressiveness does not appear to be a uniform characteristic of all tumors in HZE-irradiated animals.

Reduced inflammatory factor expression facilitates recovery after sciatic nerve injury in TLR4 mutant mice

Toll-like receptors (TLRs) are extremely significant pattern recognition receptors. When nerve injury occurs, a variety of inflammatory factors are generated, leading to an exceedingly complex micro-environment. TLRs recognize damage-associated molecular patterns. To investigate the correlation between TLR4 and recovery after sciatic nerve injury, the model of sciatic nerve injury was conducted using TLR4-mutated mice (C3H/HeJ) and wild mice (C3H/HeN). Our goal was to identify short-stage and long-stage changes after sciatic nerve injury, mainly by checking the expression changes of inflammation factors in the short-stage and the differences in the recovery of the injured sciatic nerve in the long-stage. The results show that the increase of changes in the HeN group of IL-1β, IL-6, TNF-α and MCP-1 are more obvious than in the HeJ group, with caspase1 expression higher and Nlrp3 expression lower in the former group. Further results reveal intense inflammation occurred in the HeN group showing more neutrophils and macrophages. Nlrp3 and caspase1 showed little difference by Immunohistochemistry, with Nlrp6 expression differing between the HeJ group and the HeN group. The results led us to conclude that better recovery of the injured sciatic nerve occurred in the HeJ group because the expression of GAP-43 and p75NTR was higher and had a better SFI figure. TLR4 mutation can decrease the expression of inflammatory factors and enhance the speed of recovery after sciatic nerve injury. The changes in the expression of Nlrp6, which are related to the TLR4 mutation, may influence recovery of the injured sciatic nerve. Further studies will be conducted to confirm these results.

Animal Models of Chemical Carcinogenesis: Driving Breakthroughs in Cancer Research for 100 Years

The identification of carcinogens in the workplace, diet, and environment through chemical carcinogenesis studies in animals has directly contributed to a reduction of cancer burden in the human population. Reduced exposure to these carcinogens through lifestyle changes, government regulation, or change in industry practices has reduced cancer incidence in exposed populations. In addition to providing the first experimental evidence for cancer's relationship to chemical and radiation exposure, animal models of environmentally induced cancer have and will continue to provide important insight into the causes, mechanisms, and conceptual frameworks of cancer. More recently, combining chemical carcinogens with genetically engineered mouse models has emerged as an invaluable approach to study the complex interaction between genotype and environment that contributes to cancer development. In the future, animal models of environmentally induced cancer are likely to provide insight into areas such as the epigenetic basis of cancer, genetic modifiers of cancer susceptibility, the systems biology of cancer, inflammation and cancer, and cancer prevention.

Mouse models of liver cancer

Hepatocellular carcinoma (HCC) is the sixth most common cancer worldwide, and the third leading cause of cancer mortality. The great majority of patients are not eligible for curative therapies, and therapeutic approaches for advanced disease show only limited efficacy. Difficulties to treat HCC are due to the heterogenous genetic alterations of HCC, profound alterations in the hepatic microenvironment, and incomplete understanding of HCC biology. Mouse models of HCC will be helpful to improve our understanding of HCC biology, the contributions of the specific pathways and genetic alterations to carcinogenesis. In addition, mouse models of HCC may contribute to elucidate the role of the tumor microenvironment, and serve as models for preclinical studies. As no single mouse model is appropriate to study all of the above, we discuss key features and limitations of commonly used models. Furthermore, we provide detailed protocols for select models, in which HCC is induced genetically, chemically or by transplantation of tumor cells.

Phenotypic comparison of common mouse strains developing high-fat diet-induced hepatosteatosis

Genetic predisposition and environmental factors contribute to an individual's susceptibility to develop hepatosteatosis. In a systematic, comparative survey we focused on genotype-dependent and -independent adaptations early in the pathogenesis of hepatosteatosis by characterizing C3HeB/FeJ, C57BL/6NTac, C57BL/6J, and 129P2/OlaHsd mice after 7, 14, or 21 days high-fat-diet exposure. Strain-specific metabolic responses during diet challenge and liver transcript signatures in mild hepatosteatosis outline the suitability of particular strains for investigating the relationship between hepatocellular lipid content and inflammation, glucose homeostasis, insulin action, or organelle physiology. Genetic background-independent transcriptional adaptations in liver paralleling hepatosteatosis suggest an early increase in the organ's vulnerability to oxidative stress damage what could advance hepatosteatosis to steatohepatitis. "Universal" adaptations in transcript signatures and transcription factor regulation in liver link insulin resistance, type 2 diabetes mellitus, cancer, and thyroid hormone metabolism with hepatosteatosis, hence, facilitating the search for novel molecular mechanisms potentially implicated in the pathogenesis of human non-alcoholic-fatty-liver-disease.

Hepatic lesions observed in hepatitis C virus transgenic mice infected by Helicobacter hepaticus

BACKGROUND

The heterogeneity of hepatitis C virus (HCV) infection cannot always be explained by HCV genotypes or host genetic factors, raising the issue of possible cofactors. A new form of hepatitis leading to liver cancer was discovered in 1992 in mice, owing to an infection by Helicobacter hepaticus. Moreover, several studies showed an association between the presence of HCV and Helicobacter in the liver of patients with severe liver diseases suggesting a possible synergism between the two pathogens. In an HCV transgenic mouse model with a B6C3F1 background, the combination of H. hepaticus infection and the HCV transgene resulted in a significantly greater incidence and multiplicity of preneoplastic and neoplastic liver foci in males.

OBJECTIVES

Because the mouse genetic background is a major determinant in the development of liver disease, our aim was to test the synergism between HCV and H. hepaticus infection using transgenic mice with a more sensitive genetic background to H. hepaticus infection.

METHODS

For this purpose, four groups of mice were followed up to 14 months, the presence of H. hepaticus was monitored by PCR and hepatic lesions were looked for.

RESULTS

We found that H. hepaticus, but not the HCV transgene, increased the number of hepatic lesions. The presence of carcinoma was more likely to occur on a background of hepatitis, and the overall lesions were more frequent in the presence of steatosis. The effect of the mouse genetic background was greater than the effect of the HCV transgene and was sufficient to promote lesions particularly via its sensitivity to H. hepaticus infection.

CONCLUSIONS

Genetic susceptibility may be a more important factor than expected. Indeed, the synergism between HCV and H. hepaticus infection involved in liver disease may be highly host dependent.

No inhibitory effects of (-)-epigallocatechin gallate and lycopene on spontaneous hepatotumorigenesis in C3H/HeN mice

Although several studies have indicated that (-)-epigallocatechin gallate (EGCG) and lycopene, representative dietary antioxidants, inhibit chemically induced animal tumorigenesis, only a few studies have examined the inhibitory effects of these compounds on spontaneous liver tumorigenesis in rodents. In this study, we investigated the inhibitory effects of these compounds on the formation of spontaneous liver tumors in C3H/HeN mice. We used xeroderma pigmentosum group A (XPA) gene-deficient mice to simultaneously examine whether the knockout mice could be used as a sensitive animal model. Inaddition, we examined the levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG)--a marker of reactive oxygen species-induced DNA injury--in liver tissue. Male XPA +/+, XPA +/-, and XPA -/- mice with a C3H/HeN genetic background were divided into 3 groups: control, EGCG, and lycopene. Autopsy at 18 months of age revealed that EGCG and lycopene did not exhibit obvious suppressive effects on the development of liver tumors in any XPA genotype; further, the XPA genotype did not influence any susceptibility to liver tumors. With regard to 8-OHdG levels in non-tumorous liver tissue at 8 months of age, EGCG showed no significant inhibitory effects and lycopene showed significant inhibitory effects only in XPA +/- mice. The present study demonstrates that contrary to previous reports of the inhibitory effects of EGCG and lycopene on the development of various carcinogen-induced animal tumors, these compounds exert no chemopreventive effects on spontaneous liver tumorigenesis in C3H/HeN mice. EGCG and lycopene may inhibit carcinogen-induced tumors through properties other than their antioxidant abilities.

Transcriptional changes associated with reduced spontaneous liver tumor incidence in mice chronically exposed to high dose arsenic

Exposure of male C3H mice in utero (from gestational days 8-18) to 85ppm sodium arsenite via the dams' drinking water has previously been shown to increase liver tumor incidence by 2 years of age. However, in our companion study (Ahlborn et al., 2009), continuous exposure to 85ppm sodium arsenic (from gestational day 8 to postnatal day 365) did not result in increased tumor incidence, but rather in a significant reduction (0% tumor incidence). The purpose of the present study was to examine the gene expression responses that may lead to the apparent protective effect of continuous arsenic exposure. Genes in many functional categories including cellular growth and proliferation, gene expression, cell death, oxidative stress, protein ubiquitination, and mitochondrial dysfunction were altered by continuous arsenic treatment. Many of these genes are known to be involved in liver cancer. One such gene associated with rodent hepatocarcinogenesis, Scd1, encodes stearoyl-CoA desaturase and was down-regulated by continuous arsenic treatment. An overlap between the genes in our study affected by continuous arsenic exposure and those from the literature affected by long-term caloric restriction suggests that reduction in the spontaneous tumor incidence under both conditions may involve similar gene pathways such as fatty acid metabolism, apoptosis, and stress response.

Thirty years of Mus spretus: a promising future

Extensive genetic polymorphisms in Mus spretus have ensured its widespread use in many areas of genetics. With the recent increase in the number of single nucleotide polymorphisms available for laboratory mouse strains, M. spretus is becoming less appealing, in particular for genetic mapping. Although M. spretus mice are aggressive and poor breeders, they have a bright future because they provide phenotypes unobserved in laboratory strains, and tools are available for modifying their genome and dissecting the genetic architecture of complex traits. Furthermore, they provide information on fundamental genetic questions, such as the details of evolution of genomes and speciation. Here, we examine the use of M. spretus from these perspectives. The impending completion of the M. spretus genome sequence will synergize these advantages.

Biological Basis of Differential Susceptibility to Hepatocarcinogenesis among Mouse Strains

There is a vast amount of literature related to mouse liver tumorigenesis generated over the past 60 years, not all of which has been captured here. The studies reported in this literature have generally been state of the art at the time they were carried out. A PubMed search on the topic "mouse liver tumors" covering the past 10 years yields over 7000 scientific papers. This review address several important topics related to the unresolved controversy regarding the relevance of mouse liver tumor responses observed in cancer bioassays. The inherent mouse strain differential sensitivities to hepatocarcinogenesis largely parallel the strain susceptibility to chemically induced liver neoplasia. The effects of phenobarbital and halogenated hydrocarbons in mouse hepatocarcinogenesis have been summarized because of recurring interest and numerous publications on these topics. No single simple paradigm fully explains differential mouse strain responses, which can vary more than 50-fold among inbred strains. In addition to inherent genetics, modifying factors including cell cycle balance, enzyme induction, DNA methylation, oncogenes and suppressor genes, diet, and intercellular communication influence susceptibility to spontaneous and induced mouse hepatocarcinogenesis. Comments are offered on the evaluation, interpretation, and relevance of mouse liver tumor responses in the context of cancer bioassays.

Differential selection for B-raf and Ha-ras mutated liver tumors in mice with high and low susceptibility to hepatocarcinogenesis

Activation of the Ras/Raf/MEK/ERK pathway is frequently observed in animal and human tumors. In our study, we analyzed B-raf codon 637 (formerly 624) and Ha-ras codon 61 mutations in liver tumors from C3H, B6C3F1 and C56BL mice which differ considerably with regard to their susceptibility to hepatocarcinogenesis. In total, 73% (102/140) of tumors induced by a single application of N-nitrosodiethylamine or 7,12-dimethylbenz[a]anthracene contained either B-raf or Ha-ras mutations and only <3% (4/140) were mutated in both genes. In addition, B-raf mutations were present in 76% (19/25) of early precancerous liver lesions. The prevalence of Ha-ras mutated tumors was significantly higher in the susceptible C3H and B6C3F1 mouse strains (39-50%) than in the comparatively resistant C57BL mouse (7%). B-raf mutated tumors, by contrast, were more frequent in C57BL mice (68%) than in the other two strains (17-45%). Taken together, our findings indicate that alterations affecting the Ras/Raf/MEK/ERK signalling pathway are a hallmark of carcinogen-induced liver tumors in mice. Moreover, our results show that mutational activation of B-raf in liver tumors of different mouse strains is, by contrast to Ha-ras, inversely related to their susceptibility to hepatocarcinogenesis. Although activated Ras and Raf proteins are assumed to have similar biological effects because they feed into the same signalling pathway, there seem to be subtle strain-specific differences in selection processes favouring the preferential outgrowth of either B-raf or Ha-ras mutated tumor populations in mouse liver.

Analysis of tumors arising in male B6C3F1 mice with and without AAV vector delivery to liver

The present study reports on the frequency of liver tumors observed in a gene therapy study with AAV vectors in male mice of the B6C3F1 hybrid background, which are known to have a high frequency of spontaneous liver tumors. Male mice with mutations in their Otc gene and their wild-type siblings received AAV vectors expressing either the murine Otc or the LacZ gene. Untreated control animals were included in the study. All experimental groups, including wild-type and OTC-deficient animals not treated with vector, developed liver nodules, which in some cases were due to hepatocellular carcinoma. Vector DNA was lower in tumors than in adjacent normal liver. A statistical analysis of the data did not show an association between treatment with Otc vectors and formation of tumors in OTC-deficient mice. However, mice treated with LacZ vectors showed increased risks of tumor formation and hepatocellular carcinoma relative to untreated animals or animals that had received vectors with Otc as the transgene. It appears that AAV vectors alone do not contribute to the formation of tumors in these strains of mice although the expression of LacZ alone or in combination with vector may be problematic.

Polygenic control of hepatocarcinogenesis in Copenhagen x F344 rats

Cop and CFF1 rats exhibit resistance to hepatocarcinogenesis, associated with high rates of remodeling of neoplastic lesions. We have mapped hepatocarcinogenesis susceptibility, resistance and remodeling loci affecting the number, volume and volume fraction of neoplastic nodules induced by the "resistant hepatocyte" model in male CFF2 rats. Three loci in significant linkage with the number or volume of nonremodeling lesions were identified on chromosomes 1, 4 and 18. Suggestive linkage with number or volume fraction of total, nonremodeling or remodeling lesions was found for 7 loci on chromosomes 1, 2, 13, 14 and 15. All of these loci showed significant allele-specific effects on the phenotypic traits. We also detected by analysis of variance 19 2-way interactions inducing phenotypic effects not predictable on the basis of the sum of separate effects. These novel epistatic loci were in significant linkage with the number and/or volume of total, nonremodeling or remodeling nodules. These data indicate that susceptibility to hepatocarcinogenesis in Cop rats is controlled by a complex array of genes with several gene-gene interactions and that different genetic mechanisms control remodeling and nonremodeling liver nodules. Frequent deregulation in human liver cancer of genes positioned in chromosomal segments syntenic to rat susceptibility/resistance loci suggests some similarities between the genetic mechanisms involved in hepatocarcinogenesis in rats and humans.

Rat neurological mutations cerebellar vermis defect and hobble are caused by mutations in the netrin-1 receptor gene Unc5h3

Rats homozygous for the spontaneous cerebellar vermis defect mutation (cvd) or hobble mutation (hob) exhibit cerebellar and midbrain defects, possibly as a result of abnormal neuronal migration. Both mutant rats demonstrate laminar structure abnormalities in the fused cerebellar hemispheres and ectopic cerebellar tissues in the cerebello-pontine junction. Previous genetic studies showed that cvd and hob were allelic and suggested that Unc5h3, the causative gene of the mouse rostral cerebellar malformation (rcm) mutation, was a strong candidate for both cvd and hob. Unc5h3 encodes a receptor mediating the repulsive action for Netrin-1 and has an important role during cell migration in the developing murine cerebellum. Here, we describe positional candidate cloning of cvd and hob, and identified cvd and hob mutations in the rat Unc5h3. The cvd mutation is a nucleotide conversion of G to T resulting in a premature termination at codon 451 of the UNC5H3 protein. The hob mutation is a 2-bp insertion resulting in a frame shift from codon 312 and a premature termination at codon 385 of the UNC5H3 protein. Both cvd and hob mutations are predicted to lead to truncated UNC5H3 proteins lacking their cytoplasmic region required for Netrin-Unc5h3 signaling pathway. Therefore, we conclude that Unc5h3 is causative gene of both cvd and hob mutant phenotypes. Rats homozygous for Unc5h3cvd or Unc5h3hob are the first mammalian Unc5h3 mutant model other than Unc5h3rcm/rcm mice, and will provide a useful tool for further understanding of the biological function of Unc5h3.

Haploinsufficiency of Anx7 tumor suppressor gene and consequent genomic instability promotes tumorigenesis in the Anx7(+/-) mouse

Annexin 7 (ANX7) acts as a tumor suppressor gene in prostate cancer, where loss of heterozygosity and reduction of ANX7 protein expression is associated with aggressive metastatic tumors. To investigate the mechanism by which this gene controls tumor development, we have developed an Anx7(+/-) knockout mouse. As hypothesized, the Anx7(+/-) mouse has a cancer-prone phenotype. The emerging tumors express low levels of Anx7 protein. Nonetheless, the wild-type Anx7 allele is detectable in laser-capture microdissection-derived tumor tissue cells. Genome array analysis of hepatocellular carcinoma tissue indicates that the Anx7(+/-) genotype is accompanied by profound reductions of expression of several other tumor suppressor genes, DNA repair genes, and apoptosis-related genes. In situ analysis by tissue imprinting from chromosomes in the primary tumor and spectral karyotyping analysis of derived cell lines identify chromosomal instability and clonal chromosomal aberrations. Furthermore, whereas 23% of the mutant mice develop spontaneous neoplasms, all mice exhibit growth anomalies, including gender-specific gigantism and organomegaly. We conclude that haploinsufficiency of Anx7 expression appears to drive disease progression to cancer because of genomic instability through a discrete signaling pathway involving other tumor suppressor genes, DNA-repair genes, and apoptosis-related genes.