Human hepatitis B virus and hepatocellular carcinoma. I. Experimental infection of tree shrews with hepatitis B virus

Modeling HBV Infection and Therapy in Immunodeficient NOD-Rag1-/-IL2RgammaC-null (NRG) Fumarylacetoacetate Hydrolase (FAH) Knockout Mice with Human Chimeric Liver

Chimeric mouse models with a humanized liver (Hu-HEP mice) provide a unique tool to study human hepatotropic virus diseases, including viral infection, viral pathogenesis, and anti-viral therapy. Here, we describe a detailed protocol for studying hepatitis B infection in NRG-derived fumarylacetoacetate hydrolase (FAH) knockout mice repopulated with human hepatocytes (FRG-Hu HEP mice). The procedures include (1) maintenance and genotyping of the FRG mice, (2) intrasplenic injection of primary human hepatocytes (PHH), (3) 2-(2-nitro-4-fluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) drug reduction cycling to improve human hepatocyte repopulation, (4) human albumin detection, and (5) HBV infection and detection. The method is simple and allows for highly reproducible generation of FRG-Hu HEP mice for HBV infection and therapy investigations.

Animal Models for COVID-19: Hamsters, Mouse, Ferret, Mink, Tree Shrew, and Non-human Primates

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel coronavirus causing acute respiratory tract infection in humans. The virus has the characteristics of rapid transmission, long incubation period and strong pathogenicity, and has spread all over the world. Therefore, it is of great significance to select appropriate animal models for antiviral drug development and therapeutic effect evaluation. Here, we review and compare the current animal models of SARS-CoV-2.

Tree Shrew as an Emerging Small Animal Model for Human Viral Infection: A Recent Overview

Viral infection is a global public health threat causing millions of deaths. A suitable small animal model is essential for viral pathogenesis and host response studies that could be used in antiviral and vaccine development. The tree shrew (Tupaia belangeri or Tupaia belangeri chinenesis), a squirrel-like non-primate small mammal in the Tupaiidae family, has been reported to be susceptible to important human viral pathogens, including hepatitis viruses (e.g., HBV, HCV), respiratory viruses (influenza viruses, SARS-CoV-2, human adenovirus B), arboviruses (Zika virus and dengue virus), and other viruses (e.g., herpes simplex virus, etc.). The pathogenesis of these viruses is not fully understood due to the lack of an economically feasible suitable small animal model mimicking natural infection of human diseases. The tree shrew model significantly contributes towards a better understanding of the infection and pathogenesis of these important human pathogens, highlighting its potential to be used as a viable viral infection model of human viruses. Therefore, in this review, we summarize updates regarding human viral infection in the tree shrew model, which highlights the potential of the tree shrew to be utilized for human viral infection and pathogenesis studies.

Animal Models for the Study of Hepatitis B Virus Pathobiology and Immunity: Past, Present, and Future

Hepatitis B virus (HBV) infection is a global public health problem that plagues approximately 240 million people. Chronic hepatitis B (CHB) often leads to liver inflammation and aberrant repair which results in diseases ranging from liver fibrosis, cirrhosis, to hepatocellular carcinoma. Despite its narrow species tropism, researchers have established various in vivo models for HBV or its related viruses which have provided a wealth of knowledge on viral lifecycle, pathogenesis, and immunity. Here we briefly revisit over five decades of endeavor in animal model development for HBV and summarize their advantages and limitations. We also suggest directions for further improvements that are crucial for elucidation of the viral immune-evasion strategies and for development of novel therapeutics for a functional cure.

Animal Models of Hepatitis B Virus Infection-Success, Challenges, and Future Directions

Chronic hepatitis B virus (HBV) infection affects more than 250 million people worldwide, which greatly increases the risk for terminal liver diseases, such as liver cirrhosis and hepatocellular carcinoma (HCC). Even though current approved antiviral therapies, including pegylated type I interferon (IFN) and nucleos(t)ide analogs, can effectively suppress viremia, HBV infection is rarely cured. Since HBV exhibits a narrow species tropism and robustly infects only humans and higher primates, progress in HBV research and preclinical testing of antiviral drugs has been hampered by the scarcity of suitable animal models. Fortunately, a series of surrogate animal models have been developed for the study of HBV. An increased understanding of the barriers towards interspecies transmission has aided in the development of human chimeric mice and has greatly paved the way for HBV research in vivo, and for evaluating potential therapies of chronic hepatitis B. In this review, we summarize the currently available animal models for research of HBV and HBV-related hepadnaviruses, and we discuss challenges and future directions for improvement.

Establishment of Humanized Mice for the Study of HBV

Viral hepatitis particularly Hepatitis B Virus (HBV) is still an ongoing health issue worldwide. Despite the vast technological advancements in research and development, only HBV vaccines, typically given during early years, are currently available as a preventive measure against acquiring the disease from a secondary source. In general, HBV can be cleared naturally by the human immune system if detected at low levels early. However, long term circulation of HBV in the peripheral blood may be detrimental to the human liver, specifically targeting human hepatocytes for cccDNA integration which inevitably supports HBV life cycle for the purpose of reinfection in healthy cells. Although there is some success in using nucleoside analogs or polyclonal antibodies targeting HBV surface antigens (HBsAg) in patients with acute or chronic HBV+ (CHB), majority of them would either respond only partially or succumb to the disease entirely unless they undergo liver transplants from a fully matched healthy donor and even so may not necessarily guarantee a 100% chance of survival. Indeed, in vitro/ex vivo cultures and various transgenic animal models have already provided us with a good understanding of HBV but they primarily lack human specificity or virus-host interactions in the presence of human immune surveillance. Therefore, the demand of utilizing humanized mice has increased over the last decade as a pre-clinical platform for investigating human-specific immune responses against HBV as well as identifying potential immunotherapeutic strategies in eradicating the virus. Basically, this review covers some of the recent developments and key advantages of humanized mouse models over other conventional transgenic mice platforms.

Host Diversity and Potential Transmission Pathways of SARS-CoV-2 at the Human-Animal Interface

Emerging infectious diseases present great risks to public health. The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), causing coronavirus disease 2019 (COVID-19), has become an urgent public health issue of global concern. It is speculated that the virus first emerged through a zoonotic spillover. Basic research studies have suggested that bats are likely the ancestral reservoir host. Nonetheless, the evolutionary history and host susceptibility of SARS-CoV-2 remains unclear as a multitude of animals has been proposed as potential intermediate or dead-end hosts. SARS-CoV-2 has been isolated from domestic animals, both companion and livestock, as well as in captive wildlife that were in close contact with human COVID-19 cases. Currently, domestic mink is the only known animal that is susceptible to a natural infection, develop severe illness, and can also transmit SARS-CoV-2 to other minks and humans. To improve foundational knowledge of SARS-CoV-2, we are conducting a synthesis review of its host diversity and transmission pathways. To mitigate this COVID-19 pandemic, we strongly advocate for a systems-oriented scientific approach that comprehensively evaluates the transmission of SARS-CoV-2 at the human and animal interface.

Comparing the hippocampal miRNA expression profiles of wild and domesticated Chinese tree shrews (Tupaia belangeri chinensis)

Background

The domestication of tree shrews represents an important advance in the development of standardized laboratory animals. Little is known regarding the miRNA changes that accompany the transformation of wild tree shrews into domestic tree shrews.

Results

By performing miRNA-seq analysis on wild and domestic tree shrews, we identified 2410 miRNAs and 30 differentially expressed miRNAs in the hippocampus during tree shrew domestication. A KEGG analysis of the differentially expressed genes showed that the differentially expressed miRNAs were associated with ECM-receptor interaction, the phosphatidylinositol signaling system, protein digestion and absorption, inositol phosphate metabolism, lysine degradation, fatty acid degradation and focal adhesion. Most of these pathways could be classified under environmental information processing, organismal systems and metabolism. The miRNAs exclusively expressed in wild and tame tree shrews GO enriched in terms of divergent functions. The miRNA-mRNA networks suggested that novel-m1388-5p and novel-m0746-5p might play regulatory roles in domestication of tree shrews. Real–time RT-PCR analysis was employed to verify the presence of these miRNAs.

Conclusion

We identified a number of candidate miRNA-regulated domestication genes that may represent targets for selection during the domestication of tree shrews.

Establishment and transcriptomic features of an immortalized hepatic cell line of the Chinese tree shrew

BACKGROUND

The Chinese tree shrew (Tupaia belangeri chinesis) is a rising experimental animal and has been used for studying a variety of human diseases, such as metabolic and viral infectious diseases.

METHODS

In this study, we established an immortalized tree shrew hepatic cell line, ITH6.1, by introducing the simian virus 40 large T antigen gene into primary tree shrew hepatocytes (PTHs).

RESULTS

The ITH6.1 cell line had a stable cell morphology and proliferation activity. This cell line could be infected by enterovirus 71 (EV71), but not hepatitis C virus (HCV), although the known HCV entry factors, including CD81, SR-BI, CLDN1 and OCLN, were all expressed in the PTHs and ITH6.1 of different passages. Comparison of the transcriptomic features of the PTHs and different passages of the ITH6.1 cells revealed the dynamic gene expression profiles during the transformation. We found that the DNA replication- and cell cycle-related genes were upregulated, whereas the metabolic pathway-related genes were downregulated in early passages of immortalized hepatocytes compared to the PTHs. Furthermore, expression of hepatocytes function-related genes were repressed in ITH6.1 compared to that of PTHs.

CONCLUSION

We believe these cellular expression alterations might cause the resistance of the ITH6.1 cell to HCV infection. This tree shrew liver cell line may be a good resource for the field.

KEY POINTS

• A tree shrew hepatic cell line (ITH6.1) was established. • ITH6.1 cells could be infected by EV71, but not HCV. • ITH6.1 had an altered expression profiling compared to the primary hepatocytes.

Animal models for the study of human hepatitis B and D virus infection: New insights and progress

Hepatitis B virus (HBV) is a member of the Hepadnaviridae family and infects hepatocytes, leading to liver pathology in acutely and chronically infected individuals. Co-infection with Hepatitis D virus (HDV), which requires the surface proteins of HBV to replicate, can exacerbate this disease progression. Thus, the >250 million people living with chronic HBV infection, including 13 million co-infected with HDV, would significantly benefit from an effective and affordable curative treatment. Animal models are crucial to the development of innovative disease therapies, a paradigm repeated again and again throughout the fields of immunology, neurology, reproduction, and development. Unfortunately, HBV has a highly-restricted species tropism, infecting limited species including humans, chimpanzees, and treeshrews. The first experimentally controlled studies of HBV infection were following inoculation of human volunteers in 1942, which identified the transmissibility of hepatitis through serum transfer and led to the hypothesis that the etiological agent was viral. Subsequent research in chimpanzees (Desmyter et al., 1971; Lichter, 1969) and later in other species, such as the treeshrews (Walter et al., 1996; Yan et al., 1996), further confirmed the viral origin of hepatitis B. Shortly thereafter, HBV-like viral infections were identified in woodchucks (Summers et al., 1978; Werner et al., 1979) and ducks, and much of our understanding of HBV replication can be attributed to these important models. However, with the exodus of chimpanzees from research and the limited reagents and historical data for treeshrews and other understudied species, there remains an urgent need to identify physiologically relevant models of chronic HBV infection. While large strides have been made in generating such models, particularly over the past two decades, there is still no available model that faithfully recapitulates the immunity and pathogenesis of HBV infection. Here, we discuss recent advancements in the generation of murine and non-human primate (NHP) models of HBV/HDV infection.

Cell Culture Models and Animal Models for HBV Study

Highly representative and relevant cell and mouse models are required for HBV study, including uncovering its lifecycle, investigation of the viral-host interaction, and development and evaluation of the novel antiviral therapy. During the past 40 years, both HBV cell culture models and animal models have evolved over several generations, each with significant improvement for specific purposes. In one aspect, HBV cell culture models experienced the original noninfection model including HBV plasmid DNA transfection and HBV genome integrated stable cells such as HepG2.2.15 which constitutively produces HBV virus and HepAD38 cells and its derivatives which drug-regulated HBV production. As for HBV infection models, HepaRG cells once dominated the HBV infection field for over a decade, but its complicated and labor-extensive cell differentiation procedures discouraged primary researchers from stepping in the field. The identification of human NTCP as HBV receptor evoked great enthusiasm of the whole HBV field, and its readily adaptive characteristic makes it popular in many HBV laboratories. Recombinant cccDNA (rc-cccDNA) emerged recently aiming to tackle the very basic question of how to eventually eradicate cccDNA without HBV real virus infection. In the other aspect, HBV transgenic mouse was firstly generated in the 1990s, which was helpful to decipher HBV production in vivo. However, the HBV transgenic mice were naturally immune tolerant to HBV viral products. Subsequently, a series of nonintegrated HBV mouse models were generated through plasmid hydrodynamic tail vein injection and viral vector-mediated delivery approaches, and HBV full life cycle was incomplete as cccDNA was not formed from HBV relaxed circular DNA (rcDNA). Human NTCP transgenic mouse still could not support productive HBV infection, and humanized mouse liver with human hepatocytes which supported whole HBV life cycle still dominates HBV infection in vivo, a value but expensive model until now. Other methods to empower mouse to carry HBV cccDNA were also exploited. In this chapter, we summarized the advantages and disadvantages of each model historically and provided protocols for HBV infection in HepG2-NTCP cells, HBV rc-cccDNA transfection in HepG2 cells, and HBV infection in NRG-Fah-/- liver humanized mouse.

The Regulation of HBV Transcription and Replication

Hepatitis B virus (HBV) is a major human pathogen lacking a reliable curative therapy. Current therapeutics target the viral reverse transcriptase/DNA polymerase to inhibit viral replication but generally fail to resolve chronic HBV infections. Due to the limited coding potential of the HBV genome, alternative approaches for the treatment of chronic infections are desperately needed. An alternative approach to the development of antiviral therapeutics is to target cellular gene products that are critical to the viral life cycle. As transcription of the viral genome is an essential step in the viral life cycle, the selective inhibition of viral RNA synthesis is a possible approach for the development of additional therapeutic modalities that might be used in combination with currently available therapies. To address this possibility, a molecular understanding of the relationship between viral transcription and replication is required. The first step is to identify the transcription factors that are the most critical in controlling the levels of HBV RNA synthesis and to determine their in vivo role in viral biosynthesis. Mapping studies in cell culture utilizing reporter gene constructs permitted the identification of both ubiquitous and liver-enriched transcription factors capable of modulating transcription from the four HBV promoters. However, it was challenging to determine their relative importance for viral biosynthesis in the available human hepatoma replication systems. This technical limitation was addressed, in part, by the development of non-hepatoma HBV replication systems where viral biosynthesis was dependent on complementation with exogenously expressed transcription factors. These systems revealed the importance of specific nuclear receptors and hepatocyte nuclear factor 3 (HNF3)/forkhead box A (FoxA) transcription factors for HBV biosynthesis. Furthermore, using the HBV transgenic mouse model of chronic viral infection, the importance of various nuclear receptors and FoxA isoforms could be established in vivo. The availability of this combination of systems now permits a rational approach toward the development of selective host transcription factor inhibitors. This might permit the development of a new class of therapeutics to aid in the treatment and resolution of chronic HBV infections, which currently affects approximately 1 in 30 individuals worldwide and kills up to a million people annually.

Molecular identification and antiviral function of the guanylate-binding protein (GBP) genes in the Chinese tree shrew (Tupaia belangeri chinesis)

Following viral detection and interferons (IFNs) production, several hundreds of IFN-stimulated genes (ISGs) are subsequently induced to act as direct antiviral effectors or regulators of the IFN signaling. The guanylate-binding protein (GBP) family belongs to IFN-inducible GTPases defending the host against a diverse group of invading pathogens such as parasites, bacteria and viruses. The Chinese tree shrew (Tupaia belangeri chinese) has been increasingly used as an alternative experimental animal to primates in studying viral infectious diseases. Hitherto, the tree shrew GBP family has not been characterized. In this study, we identified five tree shrew GBP genes (tGBP1, tGBP2, tGBP4, tGBP5 and tGBP7) and characterized their antiviral activities. All these tGBPs were ubiquitously expressed in heart, spleen, intestines, kidney, liver, lung and brain tissues of the tree shrew. IFN-γ treatment of tree shrew primary renal cells (TSPRCs) significantly induced the mRNA expression of tGBPs. Infections with Newcastle disease virus (NDV), encephalomyocarditis virus (EMCV) and type 1 herpes simplex virus (HSV-1) enhanced tGBPs mRNA expression in TSPRCs, but had no effect on the localization of tGBP proteins in the cytoplasm. tGBP1, but not the other four tGBPs, showed antiviral activity against vesicular stomatitis virus (VSV) and HSV-1 infections. Taken together, this study provided the first-hand information of the GBP family members in the Chinese tree shrew, which might assist the development of tree shrew animal model for infectious diseases.

A Novel Animal Model of Induced Breast Precancerous Lesion in Tree Shrew

Chinese tree shrew, an animal exhibited closer evolutionary relationship with humans compared to rodents, is getting increasingly attentions as an appealing experimental animal model for human diseases. However, a high-efficiency and stable method to establish tree shrew breast precancerous lesions model has not been clearly elucidated. Thus, the current study aimed to explore the way of establishing breast precancerous model in tree shrew and investigate the pathologic characteristics of induced breast precancerous lesions. The results indicated that 7,12-dimethylbenz(a)anthracene (DMBA) could induce breast lesions in tree shrews. However, comparing to DMBA alone, an addition of medroxyprogesterone acetate (MPA) to DMBA critically increased the rate of induced breast lesion in tree shrews. Half of induced breast lesions were intraductal papilloma and the others were atypical ductal hyperplasia. Induced lesions showed positive expression of estrogen receptor α (ERα), progesterone receptor (PR) and cytokeratin 5/6 (CK5/6), but negative expression of human epidermal growth factor receptor-2 (Her-2). The expression of B cell lymphoma-extra large (Bcl-xl) was significantly higher and the expression of B cell lymphoma 2 associated X protein (Bax) was significantly lower in the precancerous lesions (atypical ductal hyperplasia) compared to benign tumor (intraductal papilloma). These results suggest that DMBA is able to induce breast lesions in tree shrews. Combination of DMBA and MPA may be more effective to establish breast precancerous lesion tree shrew models. Tree shrew might be a promising animal model for studying the tumorogenesis of breast cancer.

Creating animal models, why not use the Chinese tree shrew (Tupaia belangeri chinensis)?

The Chinese tree shrew (Tupaia belangeri chinensis), a squirrel-like and rat-sized mammal, has a wide distribution in Southeast Asia, South and Southwest China and has many unique characteristics that make it suitable for use as an experimental animal. There have been many studies using the tree shrew (Tupaia belangeri) aimed at increasing our understanding of fundamental biological mechanisms and for the modeling of human diseases and therapeutic responses. The recent release of a publicly available annotated genome sequence of the Chinese tree shrew and its genome database (www.treeshrewdb.org) has offered a solid base from which it is possible to elucidate the basic biological properties and create animal models using this species. The extensive characterization of key factors and signaling pathways in the immune and nervous systems has shown that tree shrews possess both conserved and unique features relative to primates. Hitherto, the tree shrew has been successfully used to create animal models for myopia, depression, breast cancer, alcohol-induced or non-alcoholic fatty liver diseases, herpes simplex virus type 1 (HSV-1) and hepatitis C virus (HCV) infections, to name a few. The recent successful genetic manipulation of the tree shrew has opened a new avenue for the wider usage of this animal in biomedical research. In this opinion paper, I attempt to summarize the recent research advances that have used the Chinese tree shrew, with a focus on the new knowledge obtained by using the biological properties identified using the tree shrew genome, a proposal for the genome-based approach for creating animal models, and the genetic manipulation of the tree shrew. With more studies using this species and the application of cutting-edge gene editing techniques, the tree shrew will continue to be under the spot light as a viable animal model for investigating the basis of many different human diseases.

Comparison of the properties of neural stem cells of the hippocampus in the tree shrew and rat in vitro

Neural stem cells (NSCs) are characterized by the ability of self-renewal and capacity to proliferate and produce new nervous tissue. NSCs are capable of differentiating to three lineages of neural cells, including neurons, oligodendrocytes and astrocytes. Furthermore, hippocampal NSCs transplantation can improve the neurological deficits associated with expression of cytokines. Therefore, to compare the properties of NSCs of tree shrews and rats in vitro, NSCs from tree shrews (tsNSCs) and rats f(rNSCs) were isolated. Nestin was used as a marker to identify the cultured NSCs. Neuronal nuclei protein and glial fibrillary acidic protein (GFAP) were utilized to demonstrate the differentiation of NSCs towards neurons and astrocytes, respectively, in vitro. Furthermore, the expression of neurotrophin 3 (NT3), brain-derived neurotrophic factor (BDNF), glial cell-derived neurotrophic factor (GDNF) and transforming growth factor (TGF)β1 was also investigated in tsNSCs and rNSCs. The expression of all of the aforementioned proteins was detected using immunofluorescence methods. The results demonstrated that, after 5 days of culture, the average number of neurospheres in the cultured tsNSCs was significantly lower compared with rNSCs (P=0.0031). Additionally, compared with the rNSCs, tsNSCs exhibited an enhanced differentiation ability towards neurons. Furthermore, the expression of NT3 in the tsNSCs was higher compared with rNSCs (P<0.01), while the expression of BDNF was lower (P=0.045). However, no significant differences were observed in the expression level of GDNF and TGFβ1 between rNSCs and tsNSCs. Therefore, these results indicate that tsNSCs exhibit specific characteristics that are different from rNSCs, which provides novel information for the understanding of NSCs obtained from tree shrews. Overall, the results of the current study provide evidence to support the increased application of tree shrews as models for diseases of the central nervous system.

Studying HBV Infection and Therapy in Immune-Deficient NOD-Rag1-/-IL2RgammaC-null (NRG) Fumarylacetoacetate Hydrolase (Fah) Knockout Mice Transplanted with Human Hepatocytes

Chimeric mouse models with a humanized liver provide a unique tool to study hepatic virus diseases, including viral infection, viral pathogenesis, and antiviral therapy. Here we describe a detailed protocol for studying hepatitis B infection in NRG-derived fumarylacetoacetate hydrolase (Fah) knockout mice repopulated with human hepatocytes. The procedures include (1) maintenance and genotyping of the homozygous NRG-fah/fah mutant mice (NRG/F), (2) intrasplenic injection of human hepatocytes, (3) NTBC drug reduction cycling to improve human hepatocyte repopulation, (4) human albumin detection, and (5) HBV infection and detection. The method is simple and allows for highly reproducible generation of NRG/F-hu Hep mice for studying HBV infection and therapy.

Tree shrew (Tupaia belangeri chinensis), a novel non-obese animal model of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is becoming a severe public health problem that is affecting a large proportion of the world population. Generally, NAFLD in patients is usually accompanied by obesity, hyperglycemia, insulin resistance (IR) and type 2 diabetes (T2D), for which numerous animal models have been generated in order to explore the pathogenesis and therapies of NAFLD. On the contrary, quite a number of NAFLD subjects, especially in Asian regions, are non-obese and non-diabetic; however, few animal models are available for the research of non-obese NAFLD. Here, four approaches (here called approach 1 to 4) corresponding to the variable compositions of diets were used to treat tree shrews (Tupaia belangeri chinensis), which have a closer evolutionary relationship to primates than rodents. Analysis of plasma biochemical parameters, hepatic histology, and the expression of hepatic lipid metabolic genes revealed that all four approaches led to hepatic lipid accumulation, liver injury and hypercholesterolemia, but had no effect on body weight and adipose tissue generation, or glycemia. Hepatic gene expression in tree shrews treated by approach 4 might suggest a different or non-canonical pathway leading to hepatic steatosis. In conclusion, the tree shrew displays hepatic steatosis and dyslipidemia, but remains non-obese and non-diabetic under high energy diets, which suggests that the tree shrew may be useful as a novel animal model for the research of human non-obese NAFLD.

Extracellular Vesicles Including Exosomes Regulate Innate Immune Responses to Hepatitis B Virus Infection

The innate immune system is essential for controlling viral infection. Hepatitis B virus (HBV) persistently infects human hepatocytes and causes hepatocellular carcinoma. However, the innate immune response to HBV infection in vivo remains unclear. Using a tree shrew animal model, we showed that HBV infection induced hepatic interferon (IFN)-γ expression during early infection. Our in vitro study demonstrated that hepatic NK cells produced IFN-γ in response to HBV only in the presence of hepatic F4/80⁺ cells. Moreover, extracellular vesicles (EVs) released from HBV-infected hepatocytes contained viral nucleic acids and induced NKG2D ligand expression in macrophages by stimulating MyD88, TICAM-1, and MAVS-dependent pathways. In addition, depletion of exosomes from EVs markedly reduced NKG2D ligand expression, suggesting the importance of exosomes for NK cell activation. In contrast, infection of hepatocytes with HBV increased immunoregulatory microRNA levels in EVs and exosomes, which were transferred to macrophages, thereby suppressing IL-12p35 mRNA expression in macrophages to counteract the host innate immune response. IFN-γ increased the hepatic expression of DDX60 and augmented the DDX60-dependent degradation of cytoplasmic HBV RNA. Our results elucidated the crucial role of exosomes in antiviral innate immune response against HBV.

Hepatocarcinogenesis associated with hepatitis B, delta and C viruses

Globally, over half a billion people are persistently infected with hepatitis B (HBV) and/or hepatitis C viruses. Chronic HBV and HCV infection frequently lead to fibrosis, cirrhosis and hepatocellular carcinoma (HCC). Co-infections with hepatitis delta virus (HDV), a subviral satellite requiring HBV for its propagation, accelerates the progression of liver disease toward HCC. The mechanisms by which these viruses cause malignant transformation, culminating in HCC, remain incompletely understood, partially due to the lack of adequate experimental models for dissecting these complex disease processes in vivo.

Identification and characterization of toll-like receptors (TLRs) in the Chinese tree shrew (Tupaia belangeri chinensis)

In mammals, the toll-like receptors (TLRs) play a major role in initiating innate immune responses against pathogens. Comparison of the TLRs in different mammals may help in understanding the TLR-mediated responses and developing of animal models and efficient therapeutic measures for infectious diseases. The Chinese tree shrew (Tupaia belangeri chinensis), a small mammal with a close relationship to primates, is a viable experimental animal for studying viral and bacterial infections. In this study, we characterized the TLRs genes (tTLRs) in the Chinese tree shrew and identified 13 putative TLRs, which are orthologs of mammalian TLR1-TLR9 and TLR11-TLR13, and TLR10 was a pseudogene in tree shrew. Positive selection analyses using the Maximum likelihood (ML) method showed that tTLR8 and tTLR9 were under positive selection, which might be associated with the adaptation to the pathogen challenge. The mRNA expression levels of tTLRs presented an overall low and tissue-specific pattern, and were significantly upregulated upon Hepatitis C virus (HCV) infection. tTLR4 and tTLR9 underwent alternative splicing, which leads to different transcripts. Phylogenetic analysis and TLR structure prediction indicated that tTLRs were evolutionarily conserved, which might reflect an ancient mechanism and structure in the innate immune response system. Taken together, TLRs had both conserved and unique features in the Chinese tree shrew.

Hepatitis B virus molecular biology and pathogenesis

As obligate intracellular parasites, viruses need a host cell to provide a milieu favorable to viral replication. Consequently, viruses often adopt mechanisms to subvert host cellular signaling processes. While beneficial for the viral replication cycle, virus-induced deregulation of host cellular signaling processes can be detrimental to host cell physiology and can lead to virus-associated pathogenesis, including, for oncogenic viruses, cell transformation and cancer progression. Included among these oncogenic viruses is the hepatitis B virus (HBV). Despite the availability of an HBV vaccine, 350-500 million people worldwide are chronically infected with HBV, and a significant number of these chronically infected individuals will develop hepatocellular carcinoma (HCC). Epidemiological studies indicate that chronic infection with HBV is the leading risk factor for the development of HCC. Globally, HCC is the second highest cause of cancer-associated deaths, underscoring the need for understanding mechanisms that regulate HBV replication and the development of HBV-associated HCC. HBV is the prototype member of the Hepadnaviridae family; members of this family of viruses have a narrow host range and predominately infect hepatocytes in their respective hosts. The extremely small and compact hepadnaviral genome, the unique arrangement of open reading frames, and a replication strategy utilizing reverse transcription of an RNA intermediate to generate the DNA genome are distinguishing features of the Hepadnaviridae. In this review, we provide a comprehensive description of HBV biology, summarize the model systems used for studying HBV infections, and highlight potential mechanisms that link a chronic HBV-infection to the development of HCC. For example, the HBV X protein (HBx), a key regulatory HBV protein that is important for HBV replication, is thought to play a cofactor role in the development of HBV-induced HCC, and we highlight the functions of HBx that may contribute to the development of HBV-associated HCC.

Cholesterol induces lipoprotein lipase expression in a tree shrew (Tupaia belangeri chinensis) model of non-alcoholic fatty liver disease

Animal models are indispensible to investigate the pathogenesis and treatments of non-alcoholic fatty liver diseases (NAFLD). Altered cholesterol metabolism has been implicated into the pathogenesis of NAFLD. Here, using high fat, cholesterol and cholate diet (HFHC), we generated a novel tree shrew (Tupaia belangeri chinensis) model of NAFLD, which displayed dyslipidemia with increased levels of plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST), total cholesterol (TC), low density lipoprotein-cholesterol (LDL-c) and high density lipoprotein-cholesterol (HDL-c), but decreased level of triglycerides (TG). Liver histopathology and genes expression indicated that HFHC diet successfully induced liver steatosis to inflammation and fibrosis progressively within 10 weeks. Moreover, HFHC induced the transcriptional expression of lipoprotein lipase (lpl) in the liver, but repressed the expression of LDL receptor, and the endogenous synthesis pathway and excretion of cholesterol. Notably, Poloxamer 407 (P-407) inhibition of LPL improved the severity of steatosis and reduced inflammation. These results illustrated that LPL plays an important role in cholesterol metabolism in NAFLD, and the tree shrew may be a valuable animal model for further research into NAFLD.

Characterization of a MAVS ortholog from the Chinese tree shrew (Tupaia belangeri chinensis)

Human mitochondrial antiviral signaling protein (hMAVS, also known as IPS-1, VISA, or Cardif) is essential for antiviral innate immunity. The Chinese tree shrew (Tupaia belangeri chinenses), a close relative of primates, is emerging as a potential animal model for investigating viral infection. However, there is a lack of biological knowledge about the antiviral innate immunity of the tree shrew. In this study, we identified and characterized the function of the Chinese tree shrew MAVS gene (tMAVS). The cDNA of tMAVS was 2771 bp in length and encoded a polypeptide of 501 amino acids. Phylogenetic analyses based on the amino acid sequences revealed a closer affinity of tMAVS with those of primates. Quantitative real-time PCR analysis indicated that tMAVS mRNA was constitutively expressed in all seven tissues analyzed in this study. The tMAVS mRNA expression was rapidly and significantly increased after RNA virus infections. Ectopic-expression of tMAVS significantly potentiated the virus-triggered activation of IRF3, NF-κB and interferon-β (IFN-β), whereas knockdown of tMAVS displayed the opposite effect. Furthermore, tMAVS mutants lacking the caspase activation and recruitment (CARD) domains or the transmembrane (TM) domain were unable to induce IFN-β. Similar with hMAVS, mitochondrial localization of tMAVS was dependent on its domain. Collectively, this study revealed evolutionary conservation of the MAVS antiviral signaling pathway in the Chinese tree shrew.

Modeling hepatitis B virus infection, immunopathology and therapy in mice

Despite the availability of a preventive vaccine, chronic hepatitis B virus (HBV) infection-induced liver diseases continue to be a major global public health problem. HBV naturally infects only humans and chimpanzees. This narrow host range has hindered our ability to study the characteristics of the virus and how it interacts with its host. It is thus important to establish small animal models to study HBV infection, persistence, clearance and the immunopathogenesis of chronic hepatitis B. In this review, we briefly summarize currently available animal models for HBV research, then focus on mouse models, especially the recently developed humanized mice that can support HBV infection and immunopathogenesis in vivo. This article is part of a symposium in Antiviral Research on "From the discovery of the Australia antigen to the development of new curative therapies for hepatitis B: an unfinished story."

Chronic hepatitis B virus infection and occurrence of hepatocellular carcinoma in tree shrews (Tupaia belangeri chinensis)

BACKGROUND

Hepatitis B virus (HBV) infection has been believed as a major cause of hepatocellular carcinoma (HCC) for a long time, however, the evidences of which are mostly from clinical and epidemiological investigations while there is no evidence from animal experiments. Tree shrew (Tupaia) is a small animal closely related to primates evolutionarily, with about 8 years of lifespan. Our previous study proved that tree shrews can be chronically HBV-infected after being inoculated neonatally with HBV. The present study reports the further results from the longer-term observation of these animals.

METHODS

Neonatal tree shrews were inoculated with sera from HBV-infected patient or tree shrew. Their serum samples and liver biopsies were collected periodically for detection of HBV markers as well as for histopathological and immunohistochemical examinations. Group A consisted of six tree shrews with chronic HBV-infection, and group B consisted of nine tree shrews without chronic HBV infection.

RESULTS

Periodical examinations on serum and liver biopsies of the animals in group A showed the progress of HBV infection, and two cases of HCC occurred at their late stage of life. The courses of HBV infection and the hepatic histopathological and immunohistochemical changes in the tree shrews were similar to those in humans. In contrast, neither HCC nor obvious hepatitis histopathological change was found among the tree shrews in group B.

CONCLUSIONS

The course of HBV infection and the features of HCC discovered in tree shrews are similar to those of chronically HBV-infected humans. The tree shrew model might be used to investigate the underlying mechanisms favoring susceptibility for chronic HBV infection and disease progression.

Identification of the full-length β-actin sequence and expression profiles in the tree shrew (Tupaia belangeri)

The tree shrew (Tupaia belangeri) diverges from the primate order (Primates) and is classified as a separate taxonomic group of mammals - Scandentia. It has been suggested that the tree shrew can be used as an animal model for studying human diseases; however, the genomic sequence of the tree shrew is largely unidentified. In the present study, we reported the full-length cDNA sequence of the housekeeping gene, β-actin, in the tree shrew. The amino acid sequence of β-actin in the tree shrew was compared to that of humans and other species; a simple phylogenetic relationship was discovered. Quantitative polymerase chain reaction (qPCR) and western blot analysis further demonstrated that the expression profiles of β-actin, as a general conservative housekeeping gene, in the tree shrew were similar to those in humans, although the expression levels varied among different types of tissue in the tree shrew. Our data provide evidence that the tree shrew has a close phylogenetic association with humans. These findings further enhance the potential that the tree shrew, as a species, may be used as an animal model for studying human disorders.

Tree shrew database (TreeshrewDB): a genomic knowledge base for the Chinese tree shrew

The tree shrew (Tupaia belangeri) is a small mammal with a close relationship to primates and it has been proposed as an alternative experimental animal to primates in biomedical research. The recent release of a high-quality Chinese tree shrew genome enables more researchers to use this species as the model animal in their studies. With the aim to making the access to an extensively annotated genome database straightforward and easy, we have created the Tree shrew Database (TreeshrewDB). This is a web-based platform that integrates the currently available data from the tree shrew genome, including an updated gene set, with a systematic functional annotation and a mRNA expression pattern. In addition, to assist with automatic gene sequence analysis, we have integrated the common programs Blast, Muscle, GBrowse, GeneWise and codeml, into TreeshrewDB. We have also developed a pipeline for the analysis of positive selection. The user-friendly interface of TreeshrewDB, which is available at http://www.treeshrewdb.org, will undoubtedly help in many areas of biological research into the tree shrew.

Drug target mining and analysis of the Chinese tree shrew for pharmacological testing

The discovery of new drugs requires the development of improved animal models for drug testing. The Chinese tree shrew is considered to be a realistic candidate model. To assess the potential of the Chinese tree shrew for pharmacological testing, we performed drug target prediction and analysis on genomic and transcriptomic scales. Using our pipeline, 3,482 proteins were predicted to be drug targets. Of these predicted targets, 446 and 1,049 proteins with the highest rank and total scores, respectively, included homologs of targets for cancer chemotherapy, depression, age-related decline and cardiovascular disease. Based on comparative analyses, more than half of drug target proteins identified from the tree shrew genome were shown to be higher similarity to human targets than in the mouse. Target validation also demonstrated that the constitutive expression of the proteinase-activated receptors of tree shrew platelets is similar to that of human platelets but differs from that of mouse platelets. We developed an effective pipeline and search strategy for drug target prediction and the evaluation of model-based target identification for drug testing. This work provides useful information for future studies of the Chinese tree shrew as a source of novel targets for drug discovery research.

Tupaia belangeri as an experimental animal model for viral infection

Tupaias, or tree shrews, are small mammals that are similar in appearance to squirrels. The morphological and behavioral characteristics of the group have been extensively characterized, and despite previously being classified as primates, recent studies have placed the group in its own family, the Tupaiidae. Genomic analysis has revealed that the genus Tupaia is closer to humans than it is to rodents. In addition, tupaias are susceptible to hepatitis B virus and hepatitis C virus. The only other experimental animal that has been demonstrated to be sensitive to both of these viruses is the chimpanzee, but restrictions on animal testing have meant that experiments using chimpanzees have become almost impossible. Consequently, the development of the tupaia for use as an animal infection model could become a powerful tool for hepatitis virus research and in preclinical studies on drug development.

Strategies to inhibit entry of HBV and HDV into hepatocytes

Although there has been much research into the pathogenesis and treatment of hepatitis B virus (HBV) and hepatitis D virus (HDV) infections, we still do not completely understand how these pathogens enter hepatocytes. This is because in vitro infection studies have only been performed in primary human hepatocytes. Development of a polarizable, HBV-susceptible human hepatoma cell line and studies of primary hepatocytes from Tupaia belangeri have provided important insights into the viral and cellular factors involved in virus binding and infection. The large envelope (L) protein on the surface of HBV and HDV particles has many different functions and is required for virus entry. The L protein mediates attachment of virions to heparan sulfate proteoglycans on the surface of hepatocytes. The myristoylated N-terminal preS1 domain of the L protein subsequently binds to the sodium taurocholate cotransporting polypeptide (NTCP, encoded by SLC10A1), the recently identified bona fide receptor for HBV and HDV. The receptor functions of NTCP and virus entry are blocked, in vitro and in vivo, by Myrcludex B, a synthetic N-acylated preS1 lipopeptide. Currently, the only agents available to treat chronic HBV infection target the viral polymerase, and no selective therapies are available for HDV infection. It is therefore important to study the therapeutic potential of virus entry inhibitors, especially when combined with strategies to induce immune-mediated killing of infected hepatocytes.

Diverse interleukin-7 mRNA transcripts in Chinese tree shrew (Tupaia belangeri chinensis)

Interleukin-7 (IL7) is a pleiotropic cytokine that is actively involved in the immune system. The Chinese tree shrew (Tupaia belangeri chinensis) has been proposed as an alternative experimental animal to primates in biomedical research. However, there is a lack of biological knowledge about the immune system of the tree shrew. In this study, we cloned the IL7 gene (tIL7) in the Chinese tree shrew and quantified the expression of mRNA transcripts in eight tissues (heart, liver, spleen, lung, kidney, intestine, skeletal muscle and brain) from 20 individuals. Eleven tIL7 mRNA transcripts were identified in different tissues. The canonical form (tIL7c) had a length of 1817 bp and encoded a predicted gene product with 177 amino acids. Phylogenetic analyses based on the amino acid sequences revealed a considerably large genetic difference between tree shrew and human. Quantification of mRNA expression of transcripts tIL7c, tIL7-sv1, tIL7-sv2 and tIL7-sv3 showed that these transcripts were expressed in all tissues, albeit the expression levels varied in different tissues. Transcripts tIL7c, tIL7-sv1, and tIL7-sv2 had the lowest expression in brain, and tIL7-sv3 had a dramatically high mRNA expression in skeletal muscle and heart. The mRNA expression levels of tIL7c and tIL7-sv1 were significantly increased upon ploy(I:C) stimulation in tree shrew primary renal cells. As with human full-length IL7, tIL7c, tIL7-sv1, tIL7-sv2 and tIL7-sv3 showed similar a subcellular localization pattern. Our results identified diverse tIL7 transcripts in the Chinese tree shrew, which may play a potential role in modulating IL7-regulated biological effects.

Identification of glyceraldehyde 3-phosphate dehydrogenase sequence and expression profiles in tree shrew (Tupaia belangeri)

The tree shrews (Tupaia belangeri) diverged from the primate order (Primates) and are classified as Scandentia, a separate taxonomic group of mammals. The tree shrew has been suggested to use an animal model to study human disease but the genomic sequences of tree shrew is largely unidentified. Here we identified the full-length cDNA sequence of a housekeeping gene, Glyceraldehyde 3-phosphate Dehydrogenase (GAPDH), in tree shrew. We further constructed a phylogenetic family tree base on GAPDH molecules of various organisms and compared GAPDH sequences with human and other small experimental animals. These study revealed that tree shrew was closer to human than mouse, rat, rabbit and guinea pig. The Quantitative Reverse Transcription PCR and western blot analysis further demonstrated that GAPDH expressed in various tissues in tree shrew as a general conservative housekeeping proteins as in human. Our findings provide the novel genetic knowledge of the tree shrew and strong evidences that tree shrew can be an experimental model system to study human disorders.

Distribution of vasopressin, oxytocin and vasoactive intestinal polypeptide in the hypothalamus and extrahypothalamic regions of tree shrews

Vasopressin (VP), oxytocin (OXT) and vasoactive intestinal polypeptide (VIP) in the brain modulate physiological and behavioral processes in many vertebrates. Day-active tree shrews, the closest relatives of primates, live singly or in pairs in territories that they defend vigorously against intruding conspecifics. However, anatomy concerning peptidergic neuron distribution in the tree shrew brain is less clear. Here, we examined the distribution of VP, OXT and VIP immunoreactivity in the hypothalamus and extrahypothalamic regions of tree shrews (Tupaia belangeri chinensis) using the immunohistochemical techniques. Most of VP and OXT immunoreactive (-ir) neurons were found in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus. In addition, VP-ir or OXT-ir neurons were scattered in the preoptic area, anterior hypothalamic areas, dorsomedial hypothalamic nucleus, stria terminalis, bed nucleus of the stria terminalis and medial amygdala. Interestingly, a high density of VP-ir fibers within the ventral lateral septum was observed in males but not in females. Both VP-ir and VIP-ir neurons were found in different subdivisions of the suprachiasmatic nucleus (SCN) with partial overlap. VIP-ir cells and fibers were also scattered in the cerebral cortex, anterior olfactory nucleus, amygdala and dentate gyrus of the hippocampus. These findings provide a comprehensive description of VIP and a detailed mapping of VP and OXT in the hypothalamus and extrahypothalamic regions of tree shrews, which is an anatomical basis for the participation of these neuropeptides in the regulation of circadian behavior and social behavior.

Genome of the Chinese tree shrew

Chinese tree shrews (Tupaia belangeri chinensis) possess many features valuable in animals used as experimental models in biomedical research. Currently, there are numerous attempts to employ tree shrews as models for a variety of human disorders: depression, myopia, hepatitis B and C virus infections, and hepatocellular carcinoma, to name a few. Here we present a publicly available annotated genome sequence for the Chinese tree shrew. Phylogenomic analysis of the tree shrew and other mammalians highly support its close affinity to primates. By characterizing key factors and signalling pathways in nervous and immune systems, we demonstrate that tree shrews possess both shared common and unique features, and provide a genetic basis for the use of this animal as a potential model for biomedical research.

Experimental models and therapeutic approaches for HBV

Liver disease associated to persistent infection with the hepatitis B virus (HBV) continues to be a major health problem of global impact. In spite of the existence of an effective vaccine, approximately 360 million people are chronically infected worldwide, who are at high risk of developing liver cirrhosis and hepatocellular carcinoma. Although current therapeutic regimens can efficiently suppress viral replication, the unique replication strategies employed by HBV permit the virus to persist within the infected hepatocytes. As a consequence, relapse of viral activity is commonly observed after cessation of treatment with polymerase inhibitors. The narrow host range of HBV has hindered progresses in understanding specific steps of HBV replication and the development of more effective therapeutic strategies aiming at achieving sustained viral control and, eventually, virus eradication. This review will focus on summarizing recent advances obtained with well-established and more innovative experimental models, giving emphasis on the strength of the different systems as tools for elucidating distinct aspects of HBV persistence and for the development of new therapeutic approaches.

Suppression of hepatitis B virus replication in Tupaia hepatocytes by tumor necrosis factor alpha of Tupaia belangeri

Recently, Tupaia belangeri was used to study the full replication cycle of hepatitis B virus (HBV) in the primary hepatocyte cultures. Thus, the Tupaia model represents a suitable model to study the effects of cytokines on HBV infection. Here, Tupaia tumor necrosis factor-alpha (TNF-α) was molecularly cloned and expressed in mammalian cells. A test system for the biological activity of Tupaia TNF-α was established on the basis of its cytotoxic effect to the murine fibrosarcoma cell line L929. Recombinant Tupaia TNF-α was able to suppress HBV replication in primary Tupaia hepatocytes (PTH). However, the formation of HBV covalently closed circular DNA (cccDNA) and viral RNA was not completely prevented. Therefore, Tupaia TNF-α may contribute significantly to the control of HBV infection though it is not able to completely inhibit HBV replication alone. The characterization of this important cytokine allows further studies on its antiviral actions in the Tupaia model.

Entry of hepatitis B virus: mechanism and new therapeutic target

Entry of hepatitis B virus (HBV) into human hepatocytes constitutes the initial step in viral infection. The study of HBV entry had long been hampered by the lack of efficient cell culture systems and small animal models. The situation was greatly improved in the last decade with the development of HBV-infectible HepaRG cell line and primary Tupaia hepatocyte culture. Armed with these new tools, marked progresses have been achieved in the elucidation of the mechanism of HBV entry. Plenty of evidences indicate that the viral large surface protein (LHBs) is essential for HBV entry. Several regions in the PreS1 domain of LHBs have been verified to contribute directly to the viral attachment. In addition, a myristate moiety linked to the N-terminal glycine of PreS1 appears critical for HBV infectivity. Recently, the cysteine-rich antigenic loop of the S domain was identified as another crucial determinant for HBV infectivity. On the other hand, several cellular proteins were implicated in HBV attachment to hepatic cells, though definitive proofs are required in support to their functional involvement in HBV infection. Aiming to blocking viral entry, a couple of approaches based on acylated PreS1-derived peptides and short PreS1-binding peptides are currently under investigation, which have the potential to become novel antiviral therapeutics.

A novel approach of prophylaxis to HBV recurrence after liver transplantation

Liver transplantation (LT) in patients with hepatitis B virus (HBV) infection is associated with a high rate of graft loss and poor survival, unless re-infection can be prevented. Human hepatitis B immune globulin (HBIG) and nucleoside analogues (NA) have long been utilized to prevent re-infection. Previously, we generated a human monoclonal antibody (mAb), HB that recognizes the surface antigen of hepatitis B virus (HBV). We have constructed a secreted version of HB and cloned its genes into recombinant adeno-associated virus (AAV). We compared the efficiency of AAV vector after a single injection via intramuscular or intravenous routes without additional intervention. Then, we evaluated the activity of antibody HB in tree shrews treated with rAAV-HB and in vitro experiments. So, intramuscular injection of rAAV-HB was a suitable method for the immunoprophylaxis of HBV infection. This human antibody will be useful for the immunoprophylaxis of HBV infection.

Proteome analysis of aflatoxin B1-induced hepatocarcinogenesis in tree shrew (Tupaia belangeri chinensis) and functional identification of candidate protein peroxiredoxin II

In order to explore the proteins responsible for hepatocellular carcinoma (HCC), aflatoxin B(1)-induced hepatocarcinogenesis in tree shrew (Tupaia belangeri chinensis) was analyzed with 2-DE and MS. By comparing HCC samples with their own precancerous biopsies and HCC-surrounding tissues, a group of candidate proteins that differentially expressed in HCC were obtained. Peroxiredoxin (Prx) II, one of the candidates with distinct alteration, was further investigated and validated. Western blot and RT-PCR assays confirmed the overexpression of Prx II in both tree shrew and human HCC tissues. RNA interference for silencing Prx II was employed subsequently to explore the function and underlying mechanism of Prx II on liver cancer cell line Hep3B. Results showed the cell proliferation and clone formation decreased obviously when Prx II expression was inhibited, while the flow cytometer analysis showed the percentage of cell apoptosis enhanced. Inhibition of Prx II expression also obviously increased the generation of ROS and malondialdehyde, both are the products from peroxidation. These results imply the important role of Prx II in hepatocarcinogenesis, possibly through its function in regulating peroxidation and hereby to provide a favorable microenvironment for cancer cell surviving and progressing.

Candidate genes responsible for human hepatocellular carcinoma identified from differentially expressed genes in hepatocarcinogenesis of the tree shrew (Tupaia belangeri chinesis)

AIM

To explore gene expression profiles during hepatocarcinogenesis of the tree shrew, and to find the genes responsible for human hepatocellular carcinoma (HCC).

METHODS

Tree shrews were used as an animal model for HCC induction employing aflatoxin B(1) (AFB(1)) alone or AFB(1) plus hepatitis B virus (HBV) as etiological factors. Gene expression profiles from the tissues of HCC, HCC-surrounding liver tissues (para-HCC) and the corresponding biopsies taken from the same animals before HCC had developed (pre-HCC) were analyzed by cDNA microarray assay to identify differentially expressed genes. Two genes, CuZn-superoxide dismutase (SOD1) and glutathione S-transferase A1 (GSTA1), were further investigated by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemical (IHC) assays were done on tree shrew and human HCC samples.

RESULTS

RESULTS from the cDNA microarray analysis indicated that the gene expression profiles of HCC between AFB(1)and AFB(1) + HBV treatment groups were markedly different. A total of 11 genes, including SOD1 and GSTA1, were found changing in expression levels in all detected samples from both groups. RESULTS from RT-PCR and IHC assays indicated that mRNA and protein levels of SOD1 and GSTA1 were markedly downregulated in both tree shrew and human HCC, and downregulation of SOD1 and GSTA1 proteins in human HCC samples was closely correlated with the histopathological grading (P < 0.05).

CONCLUSION

The differentially expressed genes found in all HCC cases induced by different etiological factors among different species should be considered as good candidate genes responsible for HCC. Downregulation of SOD1 and GSTA1 might play an important role in hepatocarcinogenesis.

Efficient infection of tree shrew (Tupaia belangeri) with hepatitis C virus grown in cell culture or from patient plasma

The generation of a new, cost-effective, non-primate, small-animal model would greatly facilitate research into hepatitis C virus (HCV) pathogenesis and the development of novel therapeutic and preventative technologies to control the increasing HCV threat to public health. Native HCV from patient plasma and HCV grown in cell culture (HCVcc) were used to inoculate adult tree shrews. Each animal was inoculated with one HCV genotype. Alanine aminotransferase (ALT) levels, HCV RNA and viral load were determined in the animals before and after inoculation. For native HCV, 16/18 inoculated tree shrews (89 %) became infected; 12/16 (75 %) of these animals became chronically infected, whilst infection was resolved in the remaining four (25 %). For HCVcc, infection occurred in 10/12 inoculated tree shrews (83 %) and chronic infection was observed in two of these animals. HCVcc from Huh7 cells showed a higher infectivity than that from HeLa cells. The animals inoculated with inadequate amounts of HCV were not infected in either native HCV or HCVcc experiments. Peak viral loads reached 10(3)-10(5) international units ml(-1) in chronically infected animals. ALT level changes reflected the normal fluctuation range in most animals. Thus, tree shrews without immunosuppression can be infected efficiently by native HCV and HCVcc when the animal is inoculated with an adequate amount of single-genotype HCV.

Modeling infection with hepatitis B viruses in vivo

Hepatitis B virus (HBV) is a human-specific liver pathogen whose viral cycle and mechanisms of pathogenesis are not yet fully understood. Along with invaluable infection studies in chimpanzees, avian and mammalian HBV-related viruses continue to offer ample opportunities for studies in their natural hosts. Yet, none of these hosts are commonly used laboratory animals; the lack of reliable in vitro infection systems and convenient animal models has severely hampered progress in HBV research. The need to perform studies in HBV-permissive hepatocytes has led researchers to create new, challenging human–mouse chimera infection models. The types of animal models currently available to perform infection studies with HBV are presented and discussed in this review.