Age-related differences in amplification of covalently closed circular DNA at early times after duck hepatitis B virus infection of ducks

The p.Ser267Phe variant of sodium taurocholate cotransporting polypeptide (NTCP) supports HBV infection with a low efficiency

Sodium taurocholate cotransporting polypeptide (NTCP) is a functional receptor for human hepatitis B virus (HBV) and its satellite virus Hepatitis D virus (HDV). Physiologically, NTCP is responsible for the majority of sodium-dependent bile acids uptake by hepatocytes. The p.Ser267Phe (S267F) variant of NTCP is a single nucleotide polymorphism (SNP) previously found to cause substantial loss of ability to support HBV and HDV infection and its taurocholic acid uptake function in vitro. Intriguingly, ten individuals were identified as S267F homozygotes in population studies of chronic hepatitis B (CHB) patients. In this study, we identified new HBV isolates from one homozygous S267F mutation carrier and confirmed new isolates also use wildtype-NTCP as a cellular receptor. Furthermore, we demonstrated S267F variant of NTCP, though inefficient, is still a functional receptor for HBV entry. This study advances our understanding of NTCP-mediated HBV infection.

Efficient inhibition of duck hepatitis B virus DNA by the CRISPR/Cas9 system

Current therapeutic strategies cannot eradicate hepatitis B virus covalently closed circular DNA (HBV cccDNA), which accounts for the persistence of HBV infection. Very recently, the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR‑associated protein 9 (Cas9) system has been used as an efficient and powerful tool for viral genome editing. Given that the primary duck hepatocyte (PDH) infected with duck hepatitis B virus (DHBV) has been widely used to study human HBV infection in vitro, the present study aimed to demonstrate the targeted inhibition of DHBV DNA, especially cccDNA, by the CRISPR/Cas9 system using this model. We designed six single‑guide RNAs (sgRNA1‑6) targeting the DHBV genome. The sgRNA/Cas9 plasmid was transfected into DHBV‑infected PDHs, and then DHBV total DNA (in culture medium and PDHs) and cccDNA were quantified by reverse transcription‑quantitative polymerase chain reaction. The combined inhibition of CRISPR/Cas9 system and entecavir (ETV) was also assessed. Two sgRNAs, sgRNA4 and sgRNA6, exhibited efficient inhibition on DHBV total DNA (77.23 and 86.51%, respectively), cccDNA (75.67 and 85.34%, respectively) in PDHs, as well as DHBV total DNA in the culture medium (62.17 and 59.52%, respectively). The inhibition remained or enhanced from day 5 to day 9 following transfection. The combination of the CRISPR/Cas9 system and ETV further increased the inhibitory effect on DHBV total DNA in PDHs and culture medium, but not cccDNA. The CRISPR/Cas9 system has the potential to be a useful tool for the suppression of DHBV DNA.

Duck Hepatitis B Virus cccDNA Amplification Efficiency in Natural Infection Is Regulated by Virus Secretion Efficiency

Previous mutation based studies showed that ablating synthesis of viral envelope proteins led to elevated hepadnaviral covalently closed circular DNA (cccDNA) amplification, but it remains unknown how cccDNA amplification is regulated in natural hepadnaviral infection because of a lack of research system. In this study we report a simple procedure to prepare two identical duck hepatitis B virus inocula, but they possess 10-100-fold difference in cccDNA amplification in infected cell culture. We demonstrate that the infected cells with higher cccDNA amplification significantly reduce the virus secretion efficiency that results in higher accumulation of relaxed circular DNA (rcDNA) and DHBsAg in the cells. The infected cells with lower cccDNA amplification significantly increase the virus secretion efficiency that leads to lower intracellular rcDNA and DHBsAg accumulation. In contrast with the findings generated in the mutation based experimental system, the regulation of cccDNA amplification in natural hepadnaviral infection bypasses direct regulation of the cellular envelope proteins concentration, instead it modulates virus secretion efficiency that ultimately impacts the intracellular rcDNA concentration, an important factor determining the destination of the synthesized rcDNA in infected cells.

Rethinking the pathogenesis of hepatitis B virus (HBV) infection

Chronic hepatitis B virus (HBV) infection affects approximately 375 million people worldwide. Current antiviral treatment effectively controls, but rarely clears chronic HBV infection. In addition, a significant portion of chronic HBV infected patients are not suitable for currently available antiviral therapy, and still face higher risk for cirrhosis and hepatocellular carcinoma. The poorly understood pathogenesis of HBV infection is the main barrier for developing more effective treatment strategies. HBV has long been viewed as non-cytopathic and the central hypothesis for HBV pathogenesis lies in the belief that hepatitis B is a host specific immunity-mediated liver disease. However, this view has been challenged by the accumulating experimental and clinical data that support a model of cytopathic HBV replication. In this article we systematically review the pathogenic role of HBV replication in hepatitis B and suggest possible HBV replication related mechanisms for HBV-mediated liver injury. We propose that a full understanding of HBV pathogenesis should consider the following elements. I. Liver injury can be caused by high levels of HBV replication and accumulation of viral products in the infected hepatocytes. II. HBV infection can be either directly cytopathic, non-cytopathic, or a mix of both in an individual patient depending upon accumulation levels of viral products that are usually associated with HBV replication activity in individual infected hepatocytes.

Histopathological changes in the liver of tree shrew (Tupaia belangeri chinensis) persistently infected with hepatitis B virus

BACKGROUND

An animal model for HBV that more closely approximates the disease in humans is needed. The tree shrew (Tupaia belangeri) is closely related to primates and susceptible to HBV. We previously established that neonatal tree shrews can be persistently infected with HBV in vivo, and here present a six year follow-up histopathological study of these animals.

METHODS

Group A consists of six tree shrews with persistent HBV infection, group B consists of three tree shrews with suspected persistent HBV infection, while group C consists of four tree shrews free of HBV infection. Serum and liver tissues samples were collected periodically from all animals. HBV antigen and HBV antibodies were detected by ELISA and/or TRFIA. HBV DNA in serum and in liver biopsies was measured by FQ-PCR. Liver biopsies were applied for general histopathologic observation and scoring, immunohistochemical detections of HBsAg and HBcAg, and ultrastructural observation with electron microscope technique.

RESULTS

Hydropic, fatty and eosinophilic degeneration of hepatocytes, lymphocytic infiltration and hyperplasia of small bile ducts in the portal area were observed in group A. One animal infected with HBV for over six years showed multiple necrotic areas which had fused to form bridging necrosis and fibrosis, and megalocytosis. The hepatic histopathological scores of group A were higher than those of group B and C. The histopathological score correlated positively with the duration of infection.

CONCLUSIONS

Hepatic histopathological changes observed in chronically HBV-infected tree shrews are similar to those observed in HBV-infected humans. The tree shrew may represent a novel animal model for HBV infection.

HMGB1 gene polymorphisms in patients with chronic hepatitis B virus infection

AIM: To characterize high mobility group box chromosomal protein 1 (HMGB1) polymorphisms in patients infected with hepatitis B virus (HBV) and determine the different patterns in patient subgroups.

METHODS: A total of 1495 unrelated Han Chinese HBV carriers were recruited in this hospital-based case-control study. The HMGB1 1176 G/C polymorphism was genotyped by polymerase chain reaction-restriction fragment length polymorphism assay.

RESULTS: A significant association was observed between HMGB1 1176 G/C polymorphism and outcome of HBV infection. The subjects bearing 1176G/G genotype had an increased risk of susceptibility to chronic hepatitis B, liver cirrhosis and severe hepatitis B when compared with those bearing at least one 1176C allele.

CONCLUSION: Patients with 1176G/G genotype of HMGB1 gene are more likely to have a progressive status in HBV infection.

Duck HBV DNA copy numbers in isolated hepatocyte nuclei vary dramatically and decline during entecavir therapy

BACKGROUND

We aimed to develop a quantitative assay to measure duck HBV (DHBV) DNA in single hepatocyte nuclei from DHBV-infected animals and to observe intranuclear DHBV DNA kinetics undergoing entecavir (ETV) therapy.

METHODS

DHBV DNA in isolated nuclei was amplified by quantitative real-time PCR. Liver tissues from chronically-infected ducks with or without ETV treatment were assessed. Cell cycle phases were defined with flow cytometry in single nuclei.

RESULTS

We successfully established a quantitative assay to measure intranuclear DHBV DNA in single nuclei with high specificity, sensitivity and acceptable interassay variations. The intranuclear viral DNA copy numbers varied dramatically (2-204 copies/nuclei) in 11 ducks with active viral replication. Average intranuclear DHBV DNA copies from individual animals (7.57-57.67 copies/nuclei) significantly correlated with total intranuclear (rs=0.955, P<0.001) and serum (rs=0.745, P=0.008) viral DNA levels. The median intranuclear DHBV DNA copies in virus-positive nuclei were greater in gap 0/1 than those in gap 2/mitosis and synthesis phases (P<0.001). Median intranuclear viral DNA copies in virus-positive nuclei decreased from 21 to 6 (P<0.001) under 14-19 weeks of ETV therapy. However, subsequently, further reductions were not achieved in four animals after extended 16 week treatment (6 versus 11, P=0.034).

CONCLUSIONS

Intranuclear DHBV DNA levels varied significantly, which could be partially attributed to effects of cell cycle phases, and could be decreased by ETV therapy.

In vivo infectivity of liver extracts after resolution of hepadnaviral infection following therapy associating DNA vaccine and cytokine genes

DNA-based vaccination appears of promise for chronic hepatitis B immunotherapy, although there is an urgent need to increase its efficacy. In this preclinical study, we evaluated the therapeutic benefit of cytokine (IL-2, IFN-γ) genes co-delivery with DNA vaccine targeting hepadnaviral proteins in the chronic duck hepatitis B virus (DHBV) infection model. Then, we investigated the persistence of replication-competent virus in the livers of apparently resolved animals. DHBV carriers received four injections of plasmids encoding DHBV envelope and core alone or co-delivered with duck IL-2 (DuIL-2) or duck IFN-γ (DuIFN-γ) plasmids. After long-term (8 months) follow-up, viral covalently closed circular (ccc) DNA was analysed in duck necropsy liver samples. Liver homogenates were also tested for in vivo infectivity in neonatal ducklings. Co-delivery of DuIFN-γ resulted in significantly lower mean viremia starting from week 21. Viral cccDNA was undetectable by conventional methods in the livers of 25% and 57% of animals co-immunized with DuIL-2 and DuIFN-γ, respectively. Interestingly, inoculation of liver homogenates from 7 such apparently resolved animals, exhibiting cccDNA undetectable in Southern blotting and DHBV expression undetectable or restricted to few hepatocytes, revealed that three liver homogenates transmitted high-titre viremia (3-5×10(10) vge/mL) to naïve animals. In conclusion, our results indicate that IFN-γ gene co-delivery considerably enhances immunotherapeutic efficacy of DNA vaccine targeting hepadnaviral proteins. Importantly, we also showed that livers exhibiting only minute amounts of hepadnaviral cccDNA could induce extremely high-titre infection, highlighting the caution that should be taken in occult hepatitis B patients to prevent HBV transmission in liver transplantation context.

Experimental chronic hepatitis B infection of neonatal tree shrews (Tupaia belangeri chinensis): a model to study molecular causes for susceptibility and disease progression to chronic hepatitis in humans

BACKGROUND

Hepatitis B virus (HBV) infection continues to be an escalating global health problem. Feasible and effective animal models for HBV infection are the prerequisite for developing novel therapies for this disease. The tree shrew (Tupaia) is a small animal species evolutionary closely related to humans, and thus is permissive to certain human viral pathogens. Whether tree shrews could be chronically infected with HBV in vivo has been controversial for decades. Most published research has been reported on adult tree shrews, and only small numbers of HBV infected newborn tree shrews had been observed over short time periods. We investigated susceptibility of newborn tree shrews to experimental HBV infection as well as viral clearance over a protracted time period.

RESULTS

Forty-six newborn tree shrews were inoculated with the sera from HBV-infected patients or tree shrews. Serum and liver samples of the inoculated animals were periodically collected and analyzed using fluorescence quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, Southern blot, and immunohistochemistry. Six tree shrews were confirmed and four were suspected as chronically HBV-infected for more than 48 (up to 228) weeks after inoculation, including three that had been inoculated with serum from a confirmed HBV-infected tree shrew.

CONCLUSIONS

Outbred neonatal tree shrews can be long-term chronically infected with HBV at a frequency comparable to humans. The model resembles human disease where also a smaller proportion of infected individuals develop chronic HBV related disease. This model might enable genetic and immunologic investigations which would allow determination of underlying molecular causes favoring susceptibility for chronic HBV infection and disease establishment vs. viral clearance.

Characterization of nucleosome positioning in hepadnaviral covalently closed circular DNA minichromosomes

Hepadnaviral covalently closed circular DNA (cccDNA) exists as an episomal minichromosome in the nucleus of virus-infected hepatocytes, and serves as the transcriptional template for the synthesis of viral mRNAs. To obtain insight on the structure of hepadnaviral cccDNA minichromosomes, we utilized ducks infected with the duck hepatitis B virus (DHBV) as a model and determined the in vivo nucleosome distribution pattern on viral cccDNA by the micrococcal nuclease (MNase) mapping and genome-wide PCR amplification of isolated mononucleosomal DHBV DNA. Several nucleosome-protected sites in a region of the DHBV genome [nucleotides (nt) 2000 to 2700], known to harbor various cis transcription regulatory elements, were consistently identified in all DHBV-positive liver samples. In addition, we observed other nucleosome protection sites in DHBV minichromosomes that may vary among individual ducks, but the pattern of MNase mapping in those regions is transmittable from the adult ducks to the newly infected ducklings. These results imply that the nucleosomes along viral cccDNA in the minichromosomes are not random but sequence-specifically positioned. Furthermore, we showed in ducklings that a significant portion of cccDNA possesses a few negative superhelical turns, suggesting the presence of intermediates of viral minichromosomes assembled in the liver, where dynamic hepatocyte growth and cccDNA formation occur. This study supplies the initial framework for the understanding of the overall complete structure of hepadnaviral cccDNA minichromosomes.

Proteomic analysis of primary duck hepatocytes infected with duck hepatitis B virus

BACKGROUND

Hepatitis B virus (HBV) is a major cause of liver infection in human. Because of the lack of an appropriate cell culture system for supporting HBV infection efficiently, the cellular and molecular mechanisms of hepadnavirus infection remain incompletely understood. Duck heptatitis B virus (DHBV) can naturally infect primary duck hepatocytes (PDHs) that provide valuable model systems for studying hepadnavirus infection in vitro. In this report, we explored global changes in cellular protein expression in DHBV infected PDHs by two-dimension gel electrophoresis (2-DE) combined with MALDI-TOF/TOF tandem mass spectrometry (MS/MS).

RESULTS

The effects of hepadnavirus infection on hepatocytes were investigated in DHBV infected PDHs by the 2-DE analysis. Proteomic profile of PDHs infected with DHBV were analyzed at 24, 72 and 120 h post-infection by comparing with uninfected PDHs, and 75 differentially expressed protein spots were revealed by 2-DE analysis. Among the selected protein spots, 51 spots were identified corresponding to 42 proteins by MS/MS analysis; most of them were matched to orthologous proteins of Gallus gallus, Anas platyrhynchos or other avian species, including alpha-enolase, lamin A, aconitase 2, cofilin-2 and annexin A2, etc. The down-regulated expression of beta-actin and annexin A2 was confirmed by Western blot analysis, and potential roles of some differentially expressed proteins in the virus-infected cells have been discussed.

CONCLUSIONS

Differentially expressed proteins of DHBV infected PDHs revealed by 2-DE, are involved in carbohydrate metabolism, amino acid metabolism, stress responses and cytoskeleton processes etc, providing the insight to understanding of interactions between hepadnavirus and hepatocytes and molecular mechanisms of hepadnavirus pathogenesis.

Novel function of CD81 in controlling hepatitis C virus replication

The mechanisms of hepatitis C virus (HCV) replication remain poorly understood, and the cellular factors required for HCV replication are yet to be completely defined. CD81 is known to mediate HCV entry. Our study uncovered an unexpected novel function of CD81 in the HCV life cycle that is important for HCV RNA replication. HCV replication occurred efficiently in infected cells with high levels of CD81 expression. In HCV-infected or RNA-transfected cells with low levels of CD81 expression, initial viral protein synthesis occurred normally, but efficient replication failed to proceed. The aborted replication could be restored by the transient transfection of a CD81 expression plasmid. CD81-dependent replication was demonstrated with both an HCV infectious cell culture and HCV replicon cells of genotypes 1b and 2a. We also showed that CD81 expression is positively correlated with the kinetics of HCV RNA synthesis but inversely related to the kinetics of viral protein production, suggesting that CD81 may control viral replication by directing viral RNA template function to RNA replication. Thus, CD81 may be necessary for the efficient replication of the HCV genome in addition to its role in viral entry.

The early host innate immune response to duck hepatitis B virus infection

The early phase after hepatitis B virus infection could play a crucial role in clearance and/or persistence of the virus, particularly in neonates. This work compared the early phase of duck hepatitis B virus infection in 1-day-old (D1) and 28-day-old (D28) ducks to determine whether differences in viral or host innate immune response can be related to the difference in outcome. In the first phase, almost immediately after inoculation, virus was taken up by components of the reticulo-endothelial systems, particularly liver-specific macrophages, Kupffer cells. Very early after infection, the induction of alpha interferon by infected hepatocytes occurred and was rapidly reinforced by recruitment of effector lymphocytes, which directly or indirectly caused apoptosis, eliminating infected hepatocytes, as was seen in mature birds. In addition, a lack of lymphocytic infiltration of the liver was found in D1 ducks, which supports the suggestion that the innate immune network is less effective in D1 ducks. Taken together, these results suggest that failure of the co-ordinated innate immune response rather than a defect in induced antiviral cell-mediated immunity may be the key factor which makes baby ducks vulnerable to persistence of hepadnavirus infection.

Viral load in 1-day-old ducklings acutely infected with duck hepatitis B virus by different doses and routes of inoculation

In order to define clearly the conditions leading to the outcome of acute duck hepatitis B virus (DHBV) infection, 1-day-old Pekin ducklings were infected with DHBV by different routes and given different doses of inoculum. Groups of 24 ducklings were inoculated either intravenously via the vena cruralis, or intraperitoneally with pooled serum containing either 1.6 x 10(7) or 1.6 x 10(4) DHBV genomes. One control duck from each group was inoculated with an equal volume of normal duck serum. A sensitive and reproducible real-time polymerase chain reaction assay based on TaqMan technology was developed for the detection and quantitation of DHBV DNA in the serum and liver. DHBAg was observed in the hepatocytes by immunohistochemistry. Histological changes in the liver tissue were also observed. The results demonstrate that ducklings at each time point and in all groups developed detectable viraemia. In each group, DHBV DNA in the liver was at a lower level than in serum and the peak DNA titre was found in serum earlier than in the liver. In the low-dose groups it was always at a lower level than in the high-dose groups. The DHBV replication levels appeared to be directly related to the number of DHBAg-positive hepatocytes. The variation trends of DHBAg-positive hepatocytes were similar in the high-dose groups. Histological changes were associated with liver viral DNA levels. We suggest that this dose and route of inoculation can be used as a model to study acute DHBV infections.

Host-range and pathogenicity of hepatitis B viruses

Hepatitis B viruses are small enveloped DNA viruses referred to as Hepadnaviridae that cause transient or persistent (chronic) infections of the liver. This family is divided into two genera, orthohepadnavirus and avihepadnavirus, which infect mammals or birds as natural hosts, respectively. They possess a narrow host range determined by the initial steps of viral attachment and entry. Hepatitis B virus is the focus of biomedical research owing to its medical significance. Approximately 2 billion people have serological evidence of hepatitis B, and of these approximately 350 million people have chronic infections (World Health Organisation, Fact Sheet WHO/204, October 2000). Depending on viral and host factors, the outcomes of infection with hepatitis B virus vary between acute hepatitis, mild or severe chronic hepatitis or cirrhosis. Chronic infections are associated with an increased risk for the development of hepatocellular carcinoma.

Formation of hepatitis B virus covalently closed circular DNA: removal of genome-linked protein

Hepatitis B virus (HBV) contains a small, partially double-stranded, relaxed circular (RC) DNA genome. RC DNA needs to be converted to covalently closed circular (CCC) DNA, which serves as the template for all viral RNA transcription. As a first step toward understanding how CCC DNA is formed, we analyzed the viral and host factors that may be involved in CCC DNA formation, using transient and stable DNA transfections of HBV and the related avian hepadnavirus, duck hepatitis B virus (DHBV). Our results show that HBV CCC DNA formed in hepatoma cells was derived predominantly from RC DNA with a precise junction sequence. In contrast to that of DHBV, HBV CCC DNA formation in cultured cells was accompanied by the accumulation of a RC DNA species from which the covalently attached viral reverse transcriptase (RT) protein was removed (protein-free or PF-RC DNA). Furthermore, whereas envelope deficiency led to increased CCC DNA formation in DHBV, it resulted mainly in increased PF-RC, but not CCC, DNA in HBV, suggesting that the envelope protein(s) may negatively regulate a step in CCC DNA formation that precedes deproteination in both HBV and DHBV. Interestingly, PF-RC DNA, in contrast to RT-linked RC DNA, contained, almost exclusively, mature plus-strand DNA, suggesting that the RT protein was removed preferentially from mature RC DNA.

Hepatitis B virus replication

Hepadnaviruses, including human hepatitis B virus (HBV), replicate through reverse transcription of an RNA intermediate, the pregenomic RNA (pgRNA). Despite this kinship to retroviruses, there are fundamental differences beyond the fact that hepadnavirions contain DNA instead of RNA. Most peculiar is the initiation of reverse transcription: it occurs by protein-priming, is strictly committed to using an RNA hairpin on the pgRNA, ε, as template, and depends on cellular chaperones; moreover, proper replication can apparently occur only in the specialized environment of intact nucleocapsids. This complexity has hampered an in-depth mechanistic understanding. The recent successful reconstitution in the test tube of active replication initiation complexes from purified components, for duck HBV (DHBV), now allows for the analysis of the biochemistry of hepadnaviral replication at the molecular level. Here we review the current state of knowledge at all steps of the hepadnaviral genome replication cycle, with emphasis on new insights that turned up by the use of such cell-free systems. At this time, they can, unfortunately, not be complemented by three-dimensional structural information on the involved components. However, at least for the ε RNA element such information is emerging, raising expectations that combining biophysics with biochemistry and genetics will soon provide a powerful integrated approach for solving the many outstanding questions. The ultimate, though most challenging goal, will be to visualize the hepadnaviral reverse transcriptase in the act of synthesizing DNA, which will also have strong implications for drug development.