Hepatitis B virus (HBV) infection is a major health problem worldwide. Recent evidence suggests that some viruses can manipulate the infection process by packing specific viral and cellular components into exosomes, small nanometer-sized (30–150 nm) vesicles secreted from various cells. However, the impact of HBV replication on the content of exosomes produced by hepatocytes has not been fully delineated. In this work, an HBV-inducible cell line HepAD38 was used to directly compare changes in the protein content of exosomes secreted from HepAD38 cells with or without HBV replication. Exosomes were isolated from supernantants of HepAD38 cells cultured with or without doxycycline (dox) and their purity was confirmed by transmission electron microscopy (TEM) and Western immunoblotting assays. Ion-intensity based label-free LC-MS/MS quantitation technologies were applied to analyze protein content of exosomes from HBV replicating cells [referred as HepAD38 (dox⁻)-exo] and from HBV nonreplicating cells [referred as HepAD38 (dox⁺)-exo]. A total of 1412 exosomal protein groups were identified, among which the abundance of 35 proteins was significantly changed following HBV replication. Strikingly, 5 subunit proteins from the 26S proteasome complex, including PSMC1, PSMC2, PSMD1, PSMD7 and PSMD14 were consistently enhanced in HepAD38 (dox⁻)-exo. Bioinformatic analysis of differential exosomal proteins confirmed the significant enrichment of components involved in the proteasomal catabolic process. Proteasome activity assays further suggested that HepAD38 (dox⁻)-exo had enhanced proteolytic activity compared with HepAD38 (dox⁺)-exo. Furthermore, human peripheral monocytes incubated with HepAD38 (dox⁻)-exo induced a significantly lower level of IL-6 secretion compared with IL-6 levels from HepAD38 (dox⁺)-exo. Irreversible inhibition of proteasomal activity within exosomes restored higher production of IL-6 by monocytes, suggesting that transmission of proteasome subunit proteins by HepAD38 (dox⁻)-exo might modulate the production of pro-inflammatory molecules in the recipient monocytes. These results revealed the composition and potential function of exosomes produced during HBV replication, thus providing a new perspective on the role of exosomes in HBV-host interaction.

Currently available therapies for chronic hepatitis B virus (HBV) infection can efficiently reduce viremia, but induce hepatitis B surface antigen (HBsAg) loss in a very few patients and do not much affect the viral covalently closed circular DNA (cccDNA). To discover new agents with complementary anti-HBV effects, we performed a drug repurposing screen of 1,018 Food and Drug Administration (FDA)-approved compounds using HBV-infected primary human hepatocytes (PHH). Several compounds belonging to the family of retinoic acid receptor (RAR) agonists were identified that reduced HBsAg levels in a dose-dependent manner without significant cytotoxicity. Among them, Tazarotene exhibited the most potent anti-HBV effect with an IC₅₀ for HBsAg of less than 30 nM in PHH. The inhibitory effect was also observed in HBV-infected dHepaRG models, but not in HepG2.215 cells, and HBV genotype A to D were similarly inhibited. Tazarotene was further demonstrated to repress HBV cccDNA transcription, as determined by the levels of HBV cccDNA, RNAs and the activation of HBV promoters. Moreover, RNA-sequence analysis showed that Tazarotene did not induce an interferon response, but altered the expression of a number of genes associated with RAR and metabolic pathways. Inhibition of RARβ, but not RARα, by specific antagonist significantly attenuated the anti-HBV activity of Tazarotene, suggesting Tazarotene inhibits HBV in part through RARβ. Finally, a synergistic effect of Tazarotene and Entecavir on HBV-DNA levels was observed. Therefore, RAR agonists as represented by Tazarotene were identified as potential novel anti-HBV agents.

Over 240 million people worldwide are chronically infected with Hepatitis B Virus (HBV), a hepatotropic DNA virus with an evolutionary root of over 400 million years. Persistent HBV infection exhibits distinct and diverse phases of disease, from minimal liver pathology to fulminant Hepatitis, that vary in duration and severity among individuals. Although huge progress has been made in HBV research which has yielded an effective prophylactic vaccine and potent antiviral therapy, our understanding of its virology and immunobiology is still far from complete. For example, the recent re-discovery of serum HBV RNA in chronic Hepatitis B (CHB) patients has led to the proposal of noncanonical viral particles such as RNA virion and capsid-derived immune complex (Capsid-Antibody-Complexes, CACs) that contradict long-established basic theory. Furthermore, the existence of capsid-derived immune complex may hint at novel mechanism of HBV-induced liver disease. Here, we summarize the past and recent literature on HBV-induced immune complex. We propose that the release of capsid-derived particles by HBV has its deep evolutionary origin, and the associated complement activation serves as an indispensable trigger for intrahepatic damage and a catalyst for further cell-mediated immunopathology.

Background and Aims: HBsAg serves as an important immune-modulatory factor in chronic hepatitis B. One aspect of such modulation may act through monocytes, which are the major Ag-presenting cells taking up HBsAg. There is evidence for the encapsulation of hepatocellular microRNAs (miRNAs) by HBsAg particles, while its pathobiological significance is unclear. Here, we characterized the miRNA profile in patients with chronic hepatitis B and probed their association with liver inflammation. Approaches and Results: We collected plasma from patients that are treatment-naive with chronic hepatitis B (n = 110) and quantified total/HBsAg-enveloped miRNAs by qRT-PCR and plasma cytokines by ELISA. The biological effects of HBsAg-delivered miRNAs in monocytes were evaluated using multiple approaches. The clinical significance of candidate miRNAs and cytokines was corroborated in patients with HBV-associated advanced liver diseases. The plasma miRNA profile showed 2 major clusters, one significantly associated with HBsAg titer and the other correlated with liver inflammation. Among HBsAg-carried miRNAs, miR-939 displayed the most significant correlation with IL-8. Mechanistically, miR-939 in subviral particles enters monocytes and significantly augments IL-8 production through the mitogen-activated protein kinase (MAPK) p38 signaling pathway. Finally, the findings that miR-939 positively correlated with IL-8 level and inflammation/fibrosis stage in the cohort of HBV-associated advanced liver diseases support its causative role in the progression of liver diseases. Conclusions: HBsAg particles carry hepatocellular miRNAs, including miR-939, which enter monocytes and alter their functional status, such as IL-8 secretion. Our findings demonstrate that the HBsAg-miR-939-IL-8 axis may play a crucial role in HBV-induced hepatic necro-inflammation and the progression of advanced liver diseases.

Extracellular HBV RNA has been detected in both HBV-replicating cell culture media and sera from chronic hepatitis B (CHB) patients, but its exact origin and composition remain controversial. Here, we demonstrated that extracellular HBV RNA species were of heterogeneous lengths, ranging from the length of pregenomic RNA to a few hundred nucleotides. In cell models, these RNAs were predominantly associated with naked capsids although virions also harbored a minority of them. Moreover, HBV RNAs in hepatitis B patients’ blood circulation were localized in unenveloped capsids in the form of capsid-antibody-complexes (CACs) and in virions. Furthermore, we showed that extracellular HBV RNAs could serve as template for viral DNA synthesis. In conclusion, extracellular HBV RNAs mainly consist of pgRNA or the pgRNA species degraded by the RNase H domain of the polymerase in the process of viral DNA synthesis and circulate as CACs and virions. Their presence in the blood circulation of CHB patients may be exploited to develop novel biomarkers for HBV persistence.

Background: Although immune complex formation is widely acknowledged as the etiological agent for the development of systemic lupus erythematosus, polyarteritis nodosa, reactive arthritis, etc., its roles in chronic hepatitis are less understood. This study aims to compare the immunohistochemistry profile of immune complex deposition in patients with chronic hepatitis B (CHB) and autoimmune hepatitis (AIH). Methods: Immunohistochemistry of C4d, a widely used marker for complement deposition was employed on liver biopsies from 72 and 15 patients with CHB and AIH, respectively. Statistical analysis was performed to analyze its prevalence and its association with a range of clinical and histological parameters. Results: Among the 15 AIH biopsies examined, C4d deposition was observed in 11 cases (73.3%), the majority of which showed a periportal staining pattern (10/11). In CHB, 61 (84.7%) of 72 cases tested positive for C4d, which did not differ significantly with that of AIH. While the periportal pattern was predominantly observed in CHB cases, positive staining in central veins, sinusoids, and hepatic parenchyma were also documented. In particular, C4d deposition is significantly associated with elevated serum ALT and liver inflammation in CHB. Of note, in specimens with a patchy parenchymal C4d staining pattern, a spatially correlated HBsAg IHC signal was observed in adjacent sections from the same tissue. Conclusions: These data suggest an involvement of immune complex-mediated immunopathy in autoimmune hepatitis and HBV-induced hepatitis. The positive intrahepatic C4d signal was associated with heightened liver inflammation. The colocalization of the C4d signal on hepatocytes with HBsAg strongly suggests a causal relationship between viral activity and complement deposition. These observations align with our recent evidence implicating the contribution of capsid–antibody complexes in the pathogenesis of CHB.