Acute hepatitis B of genotype H resulting in persistent infection

Exploring the tolerable region for HiBiT tag insertion in the hepatitis B virus genome

A cell culture system that allows the reproduction of the hepatitis B virus (HBV) life cycle is indispensable to exploring novel anti-HBV agents. To establish the screening system for anti-HBV agents, we exploited the high affinity and bright luminescence (HiBiT) tag and comprehensively explored the regions in the HBV genome where the HiBiT tag could be inserted. The plasmids for the HiBiT-tagged HBV molecular clones with a 1.38-fold HBV genome length were prepared. The HiBiT tag was inserted into five regions: preS1, preS2, hepatitis B e (HBe), hepatitis B X (HBx), and hepatitis B polymerase (HB pol). HiBiT-tagged HBVs were obtained by transfecting the prepared plasmids into sodium taurocholate cotransporting polypeptide-transduced HepG2 (HepG2/NTCP) cells, and their infectivity was evaluated in human primary hepatocytes and HepG2/NTCP cells. Among the evaluated viruses, the infection of HiBiT-tagged HBVs in the preS1 or the HB pol regions exhibited a time-dependent increase of the hepatitis B surface antigen (HBsAg) level after infection to HepG2/NTCP cells as well as human primary hepatocytes. Immunostaining of the hepatitis B core (HBc) antigen in infected cells confirmed these viruses are infectious to those cells. However, the time-dependent increase of the HiBiT signal was only detected after infection with the HiBiT-tagged HBV in the preS1 region. The inhibition of this HiBiT-tagged HBV infection in human primary hepatocytes and HepG2/NTCP cells by the preS1 peptide could be detected by measuring the HiBiT signal. The infection system with the HiBiT-tagged HBV in HepG2/NTCP cells facilitates easy, sensitive, and high-throughput screening of anti-HBV agents and will be a useful tool for assessing the viral life cycle and exploring antiviral agents.

IMPORTANCE

Hepatitis B virus (HBV) is the principal causative agent of chronic hepatitis. Despite the availability of vaccines in many countries, HBV infection has spread worldwide and caused chronic infection. In chronic hepatitis B patients, liver inflammation leads to cirrhosis, and the accumulation of viral genome integration into host chromosomes leads to the development of hepatocellular carcinoma. The currently available treatment strategy cannot expect the eradication of HBV. To explore novel anti-HBV agents, a cell culture system that can detect HBV infection easily is indispensable. In this study, we examined the regions in the HBV genome where the high affinity and bright luminescence (HiBiT) tag could be inserted and established an HBV infection system to monitor infection by measuring the HiBiT signal by infecting the HiBiT-tagged HBV in sodium taurocholate cotransporting polypeptide-transduced HepG2 (HepG2/NTCP) cells. This system can contribute to screening for novel anti-HBV agents.

Host and HBV Interactions and Their Potential Impact on Clinical Outcomes

Hepatitis B virus (HBV) is a challenge for global health services, affecting millions and leading thousands to end-stage liver disease each year. This comprehensive review explores the interactions between HBV and the host, examining their impact on clinical outcomes. HBV infection encompasses a spectrum of severity, ranging from acute hepatitis B to chronic hepatitis B, which can potentially progress to cirrhosis and hepatocellular carcinoma (HCC). Occult hepatitis B infection (OBI), characterized by low HBV DNA levels in hepatitis B surface antigen-negative individuals, can reactivate and cause acute hepatitis B. HBV genotyping has revealed unique geographical patterns and relationships with clinical outcomes. Moreover, single nucleotide polymorphisms (SNPs) within the human host genome have been linked to several clinical outcomes, including cirrhosis, HCC, OBI, hepatitis B reactivation, and spontaneous clearance. The immune response plays a key role in controlling HBV infection by eliminating infected cells and neutralizing HBV in the bloodstream. Furthermore, HBV can modulate host metabolic pathways involved in glucose and lipid metabolism and bile acid absorption, influencing disease progression. HBV clinical outcomes correlate with three levels of viral adaptation. In conclusion, the clinical outcomes of HBV infection could result from complex immune and metabolic interactions between the host and HBV. These outcomes can vary among populations and are influenced by HBV genotypes, host genetics, environmental factors, and lifestyle. Understanding the degrees of HBV adaptation is essential for developing region-specific control and prevention measures.

METTL16 regulates m6A methylation on chronic hepatitis B associated gene HLA-DPB1 involved in liver fibrosis

The role of genetic factors in the occurrence and progression of CHB (CHB) is still not fully explored. In recent years, genome-wide association studies on CHB patients have demonstrated that a large number of CHB-associated single nucleotide polymorphisms exist in the gene intron, which may regulate expression at the transcriptional level. Modification of RNA m⁶A methylation is one of the key mechanisms regulating gene expression. Here we show that METTL16, an m⁶A regulator involved in mRNA intron splicing, is differentially expressed in CHB the tissue of patients who has definite diagnosis of mild and severe fibrosis. At the same time, there are also significant differences in the expression of CHB-associated genes such as HLA-DPA1 and HLA-DPB1. The expression of HLA-DPB1 is related to METTL16. Furthermore, analyses of RNA binding of METTL16 and HLA-DPB1 show that the silencing of METTL16 in astrocytes downregulates m⁶A and expression of HLA-DPB1. In conclusion, METTL16 participates in the progression of CHB fibrosis by regulating the m⁶A level and expression of HLA-DPB1.

Evolutionary history of hepatitis B virus genotype H

Hepatitis B virus genotype H (HBV-H) molecular evolution was studied by comparing all published whole-genome sequences. Bayesian coalescent analysis was performed to estimate phylogenetic relationships, time to the most recent common ancestor (tMRCA), and viral population dynamics along the time. Phylogenetic tree demonstrated two main clades or lineages: HBV-H I (with sequences from Central and North America) and HBV-H II (with sequences from North and South America, and Asia). HBV-H II had more genome sequences (n = 26; 83.9%), including one specific subclade with all sequences outside of the Americas. Overall HBV-H tMRCA dated back to 1933 (95% highest posterior density interval [HPD 95%]: 1875-1957) with a very probable origin in Mexico and posterior dissemination to other American and Asian countries. The temporal analysis demonstrated that HBV-H I spread only in Mexico and the neighbor country of Nicaragua probably in the 1960s to the 1970s (1968; HPD 95%: 1908-1981), while HBV-II disseminated to other American and Asian countries around one decade later (1977; HPD 95%: 1925-1985). The phylogeographic analysis reinforced the Mexican origin of this genotype. The whole HBV-H population increased from the 1980s to the 2000s. In conclusion, HBV-H has two main lineages with a common origin in Mexico approximately nine decades ago.

N-Terminal PreS1 Sequence Regulates Efficient Infection of Cell-Culture-Generated Hepatitis B Virus

BACKGROUND AND AIMS

An efficient cell-culture system for hepatitis B virus (HBV) is indispensable for research on viral characteristics and antiviral reagents. Currently, for the HBV infection assay in cell culture, viruses derived from HBV genome-integrated cell lines of HepG2.2.15 or HepAD-38 are commonly used. However, these viruses are not suitable for the evaluation of polymorphism-dependent viral characteristics or resistant mutations against antiviral reagents. HBV obtained by the transient transfection of the ordinary HBV molecular clone has limited infection efficiencies in cell culture.

APPROACH AND RESULTS

We found that an 11-amino-acid deletion (d11) in the preS1 region enhances the infectivity of cell-culture-generated HBV (HBVcc) to sodium taurocholate cotransporting polypeptide-transduced HepG2 (HepG2/NTCP) cells. Infection of HBVcc derived from a d11-introduced genotype C strain (GTC-d11) was ~10-fold more efficient than infection of wild-type GTC (GTC-wt), and the number of infected cells was comparable between GTC-d11- and HepG2.2.15-derived viruses when inoculated with the same genome equivalents. A time-dependent increase in pregenomic RNA and efficient synthesis of covalently closed circular DNA were detected after infection with the GTC-d11 virus. The involvement of d11 in the HBV large surface protein in the enhanced infectivity was confirmed by an HBV reporter virus and hepatitis D virus infection system. The binding step of the GTC-d11 virus onto the cell surface was responsible for this efficient infection.

CONCLUSIONS

This system provides a powerful tool for studying the infection and propagation of HBV in cell culture and also for developing the antiviral strategy against HBV infection.

Hepatitis B Virus Genotype-Dependent Vulnerability of Infected Cells to Immune Reaction in the Early Phase of Infection

Infection with hepatitis B virus (HBV) genotype (GT)-A has been reported to predispose patients to chronic infection. To explore the immune responses in infection with different HBV genotypes and clarify the genotype-dependent pathogenicity, a system mimicking the immune reaction during the early phase of HBV infection is indispensable. To this end, we established a coculture system with the replication-competent HBV molecular clone-transfected HepG2 cells and immortalized human natural killer (NK) cells, NK-92MI. Using this system, we evaluated HBV genotype dependency in NK functions and cell death of HBV positive HepG2 cells induced by NK cells or administration of tumor necrosis factor (TNF) by use of flow cytometry. After coculture with NK cells, we found that GT-A-positive HepG2 cells exhibited lower susceptibility to NK cell-induced cell death than GT-B- or GT-C-positive HepG2 cells. The NK responses of degranulation and cytokine production were not different among transfected HBV genotypes in cocultured cells. The expression levels of death receptors in HBV-transfected HepG2 cells were not different. In GT-A-positive cells, a similar low susceptibility was detected by the external administration of TNF, although relatively higher susceptibility was observed in GT-B- and GT-C-positive cells than in GT-A-positive cells. The activation of caspase signaling was revealed to be responsible for this genotype-dependent susceptibility. In conclusion, our results indicate that the HBV genotype does not influence the NK cell function itself but rather cell vulnerability through the TNF signal pathway. This observation may explain the high chronicity rate of HBV GT-A strains even in adult infections.

Resistance mutations of hepatitis B virus in entecavir-refractory patients

The emergence of resistance mutations in the reverse transcriptase gene of hepatitis B virus (HBV) is associated with treatment failure. Entecavir (ETV) is one of the most potent anti‐HBV reagents; it has a very low resistance rate and is used as the first‐line treatment for chronic hepatitis B. In this study, we isolated HBVs in 4 ETV‐refractory patients (2 with viral breakthrough, 1 with partial virological response, and 1 with flare‐up) and assessed ETV resistance using replication‐competent 1.38‐fold HBV genome‐length molecular clones. The full genome sequences of infected HBVs in ETV‐refractory patients were determined. The HBV molecular clones were generated with the patient‐derived sequences. After transfection of these molecular clones into HepG2 cells, viral replications and ETV susceptibilities were evaluated by measuring the amount of intracellular core‐particle‐associated HBV DNA using Southern blotting and real‐time polymerase chain reaction. Among these cases, ETV‐resistant variants were detected in 2 patients with viral breakthrough and responsible amino acid mutations in reverse transcriptase were successfully identified in these variants. No ETV‐resistant mutation was detected in the other cases. The identified ETV‐resistant mutations did not confer resistance to tenofovir disoproxil fumarate. Conclusion: The HBV replication model with patient‐derived sequences is useful for assessing replication efficiency, susceptibility to anti‐HBV reagents, and responsible resistance mutations and can aid in choosing the appropriate treatment strategy for treatment‐failure cases of chronic hepatitis B. (Hepatology Communications 2017;1:110‐121)