Cholesterol depletion of hepatoma cells impairs hepatitis B virus envelopment by altering the topology of the large envelope protein

Statins in Chronic Liver Disease: Review of the Literature and Future Role

Chronic liver disease (CLD) is a major contributor to global mortality, morbidity, and healthcare burden. Progress in pharmacotherapeutic for CLD management is lagging given its impact on the global population. While statins are indicated for the management of dyslipidemia and cardiovascular disease, their role in CLD prevention and treatment is emerging. Beyond their lipid-lowering effects, their liver-related mechanisms of action are multifactorial and include anti-inflammatory, antiproliferative, and immune-protective effects. In this review, we highlight what is known about the clinical benefits of statins in viral and nonviral etiologies of CLD and hepatocellular carcinoma (HCC), and explore key mechanisms and pathways targeted by statins. While their benefits may span the spectrum of CLD and potentially HCC treatment, their role in CLD chemoprevention is likely to have the largest impact. As emerging data suggest that genetic variants may impact their benefits, the role of statins in precision hepatology will need to be further explored.

Cholesterol depletion inhibits rabies virus infection by restricting viral adsorption and fusion

Rabies is an ancient zoonotic disease caused by the rabies virus (RABV), and a sharp increase in rabies cases and deaths were observed following the COVID-19 pandemic, indicating that it still poses a severe public health threat in most countries in the world. Cholesterol is one of the major lipid components in cells, and the exact role of cholesterol in RABV infection remains unclear. In this study, we initially observed that cellular cholesterol levels were significantly elevated in RABV infected cells, while cholesterol depletion by using methyl-β-cyclodextrin (MβCD) could restrict RABV entry. We further found that decreasing the cholesterol level of the viral envelope could change the bullet-shaped morphology of RABV and dislodge the glycoproteins on its surface to affect RABV entry. Moreover, the depletion of cholesterol could decrease lysosomal cholesterol accumulation to inhibit RABV fusion. Finally, it was found that the depletion of cholesterol by MβCD was due to the increase of oxygen sterol production in RABV-infected cells and the enhancement of cholesterol efflux by activating liver X receptor alpha (LXRα). Together, our study reveals a novel role of cholesterol in RABV infection, providing new insight into explore of effective therapeutics for rabies.

The "humanized" N-glycosylation pathway in CRISPR/Cas9-edited Nicotiana benthamiana significantly enhances the immunogenicity of a S/preS1 Hepatitis B Virus antigen and the virus-neutralizing antibody response in vaccinated mice

The recent SARS-CoV-2 pandemic has taught the world a costly lesson about the devastating consequences of viral disease outbreaks but also, the remarkable impact of vaccination in limiting life and economic losses. Vaccination against human Hepatitis B Virus (HBV), a major human pathogen affecting 290 million people worldwide, remains a key action towards viral hepatitis elimination by 2030. To meet this goal, the development of improved HBV antigens is critical to overcome non-responsiveness to standard vaccines based on the yeast-produced, small (S) envelope protein. We have recently shown that combining relevant immunogenic determinants of S and large (L) HBV proteins in chimeric antigens markedly enhances the anti-HBV immune response. However, the demand for cost-efficient, high-quality antigens remains challenging. This issue could be addressed by using plants as versatile and rapidly scalable protein production platforms. Moreover, the recent generation of plants lacking β-1,2-xylosyltransferase and α-1,3-fucosyltransferase activities (FX-KO), by CRISPR/Cas9 genome editing, enables production of proteins with "humanized" N-glycosylation. In this study, we investigated the impact of plant N-glycosylation on the immunogenic properties of a chimeric HBV S/L vaccine candidate produced in wild-type and FX-KO Nicotiana benthamiana. Prevention of β-1,2-xylose and α-1,3-fucose attachment to the HBV antigen significantly increased the immune response in mice, as compared with the wild-type plant-produced counterpart. Notably, the antibodies triggered by the FX-KO-made antigen neutralized more efficiently both wild-type HBV and a clinically relevant vaccine escape mutant. Our study validates in premiere the glyco-engineered Nicotiana benthamiana as a substantially improved host for plant production of glycoprotein vaccines.

The Association between Statins and Liver Cancer Risk in Patients with Heart Failure: A Nationwide Population-Based Cohort Study

Heart failure (HF) and cancer have similar risk factors. HMG-CoA reductase inhibitors, also known as statins, are chemoprotective agents against carcinogenesis. We aimed to evaluate the chemoprotective effects of statins against liver cancer in patients with HF. This cohort study enrolled patients with HF aged ≥20 years between 1 January 2001 and 31 December 2012 from the National Health Insurance Research Database in Taiwan. Each patient was followed to assess liver cancer risk. A total of 25,853 patients with HF were followed for a 12-year period; 7364 patients used statins and 18,489 did not. The liver cancer risk decreased in statin users versus non-users (adjusted hazard ratio (aHR) = 0.26, 95% confidence interval (CI): 0.20-0.33) in the entire cohort in the multivariate regression analysis. In addition, both lipophilic and hydrophilic statins reduced the liver cancer risk in patients with HF (aHR 0.34, 95% CI: 0.26-0.44 and aHR 0.42, 95% CI: 0.28-0.54, respectively). In the sensitivity analysis, statin users in all dose-stratified subgroups had a reduced liver cancer risk regardless of age, sex, comorbidity, or other concomitant drug use. In conclusion, statins may decrease liver cancer risk in patients with HF.

Sac1 phosphatidylinositol 4-phosphate phosphatase is a novel host cell factor regulating hepatitis B virus particles assembly and release

The life-cycle of the Hepatitis B Virus (HBV), an enveloped DNA virus affecting the lives of more than 296 million chronicallyinfected people, is tightly dependent on the lipid metabolism of the host cell. Fatty acids and cholesterol are among the lipid factors with documented roles in regulating HBV replication and infection, respectively, but little is known about the phosphoinositide metabolism in these processes. In this study, we investigated the role of Sac1, a highly conserved phosphatidylinositol-4-phosphate (PI4P) phosphatase, with essential functions in phospholipid metabolism, in HBV assembly, and release. PI4P is one of the most abundant cellular phosphoinositide with complex functions at the level of the secretory pathway. Owing to the highly specific phosphatase activity toward PI4P, Sac1 controls the levels and restricts the localization of this lipid particularly at the trans-Golgi network, where it regulates sphingolipid synthesis, proteins sorting, and vesicles budding, by recruiting specific adaptor proteins. As a complete loss of Sac1 function compromises cell viability, in this work, we first developed and characterized several HBV replication-permissive cellular models with a moderate, transient, or stable downregulation of Sac1 expression. Our results show that Sac1 depletion in hepatic cells results in increased levels and redistribution of intracellular PI4P pools and impaired trafficking of the HBV envelope proteins to the endosomal vesicular network. Importantly, virus envelopment and release from these cells are significantly inhibited, revealing novel roles for Sac1, as a key host cell factor regulating morphogenesis of a DNA virus.

Efficient cellular and humoral immune response and production of virus-neutralizing antibodies by the Hepatitis B Virus S/preS116-42 antigen

Despite the availability of improved antiviral therapies, infection with Hepatitis B virus (HBV) remains a3 significant health issue, as a curable treatment is yet to be discovered. Current HBV vaccines relaying on the efficient expression of the small (S) envelope protein in yeast and the implementation of mass vaccination programs have clearly contributed to containment of the disease. However, the lack of an efficient immune response in up to 10% of vaccinated adults, the controversies regarding the seroprotection persistence in vaccine responders and the emergence of vaccine escape virus mutations urge for the development of better HBV immunogens. Due to the critical role played by the preS1 domain of the large (L) envelope protein in HBV infection and its ability to trigger virus neutralizing antibodies, including this protein in novel vaccine formulations has been considered a promising strategy to overcome the limitations of S only-based vaccines. In this work we aimed to combine relevant L and S epitopes in chimeric antigens, by inserting preS1 sequences within the external antigenic loop of S, followed by production in mammalian cells and detailed analysis of their antigenic and immunogenic properties. Of the newly designed antigens, the S/preS1^16–42 protein assembled in subviral particles (SVP) showed the highest expression and secretion levels, therefore, it was selected for further studies in vivo. Analysis of the immune response induced in mice vaccinated with S/preS1^16–42- and S-SVPs, respectively, demonstrated enhanced immunogenicity of the former and its ability to activate both humoral and cellular immune responses. This combined activation resulted in production of neutralizing antibodies against both wild-type and vaccine-escape HBV variants. Our results validate the design of chimeric HBV antigens and promote the novel S/preS1 protein as a potential vaccine candidate for administration in poor-responders to current HBV vaccines.

Atorvastatin Rapidly Reduces Hepatitis B Viral Load in Combination with Tenofovir: A Prospective Clinical Trial

Objective and Aim. Atorvastatin inhibits cholesterol synthesis which is critically important in the formation of the viral envelope and secretion. The efficacy and safety of giving atorvastatin (40 mg/day) as an adjunct to tenofovir in the treatment of hepatitis B (HBV) were assessed. Method. In this single-blind clinical trial, 40 patients with active chronic hepatitis B were randomly allocated to treatment or control groups. The treatment group received the standard treatment for chronic HBV (300 mg tenofovir twice a day) along with 40 mg/day atorvastatin for 12 months, while the control group received a placebo once daily in addition to the standard tenofovir regimen. Serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and HBV DNA copy numbers were measured at the beginning of the treatment and 1, 3, 6, 9, 12 months later. Results. One month after starting the treatment, the HBV copy number in the atorvastatin + tenofovir-treated group was significantly lower, by 200×, compared with the control group. After three months of the treatment, there was no detectable HBV DNA in 50% of the atorvastatin + tenofovir-treated group compared with 30% in the control group. The half-life of plasma viral load was 2.03 and 3.32 months in the atorvastatin + tenofovir-treated and control groups, respectively. No adverse events due to taking atorvastatin were observed. Conclusions. The combination of atorvastatin with tenofovir increased antiviral activity and led to a faster recovery from viral infection. Therefore, this modality can be recommended as a safe combination therapy for chronic hepatitis B patients.

Hepatocyte steatosis inhibits hepatitis B virus secretion via induction of endoplasmic reticulum stress

The effects of hepatocyte steatosis on hepatitis B virus (HBV) DNA replication and HBV-related antigen secretion are incompletely understood. The aims of this study are to explore the effects and mechanism of hepatocyte steatosis on HBV replication and secretion. Stearic acid (SA) and oleic acid (OA) were used to induce HepG2.2.15 cell steatosis in this study. The expressions of glucose-regulated protein 78 (GRP78), phosphorylation of protein kinase R-like endoplasmic reticulum (ER) kinase (p-PERK), and eukaryotic translation initiation factor 2α (p-eIF2α) were detected by Western blotting (WB). HBV DNA, HBsAg, and HBeAg in the supernatant were determined by real-time fluorescent polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay. Intracellular HBV DNA, HBsAg level, and HBV RNA were measured by real-time fluorescent PCR, WB, and real-time quantitative reverse transcriptase-PCR, respectively. The results showed that SA and OA significantly increased intracellular lipid droplets and triglyceride levels. SA and OA significantly induced GRP78, p-PERK, and p-eIF2α expressions from 24 to 72 h. 4-phenylbutyric acid (PBA) alleviated ER stress induced by SA. SA promoted intracellular HBsAg and HBV DNA accumulation; however, it inhibited the transcript of HBV 3.5 kb mRNA and S mRNA. The secretion of HBsAg and HBV DNA inhibited by SA or OA could be partially restored by pretreatment with PBA but not by inhibiting GRP78 expression with siRNA. Hepatocyte steatosis inhibits HBsAg and HBV DNA secretion via induction of ER stress in hepatocytes, but not via induction of GRP78.

Hepatocyte Endoplasmic Reticulum Stress Inhibits Hepatitis B Virus Secretion and Delays Intracellular Hepatitis B Virus Clearance After Entecavir Treatment

Background: The aim of this study was to explore the effects of endoplasmic reticulum (ER) stress on hepatitis B virus (HBV) replication and the antiviral effect of entecavir (ETV).

Methods: Thapsigargin (TG) and stearic acid (SA) were used to induce ER stress in HepG2.2.15 cells and HepAD38 cells that contained an integrated HBV genome, while ETV was used to inhibit HBV replication. The expression levels of glucose-regulated protein 78 (GRP78) and phosphorylated eukaryotic translation initiation factor 2 subunit alpha (p-eIF2α) were measured by western blotting. Intracellular HBV DNA was determined by qPCR; HBsAg by western blotting; HBV RNA by real-time RT-qPCR; HBsAg and HBeAg in supernatants by enzyme-linked immunosorbent assay (ELISA); and HBV DNA in supernatants by qPCR.

Results: TG and SA induced ER stress in HepG2.2.15 cells and HepAD38 cells from 12 to 48 h post treatment. However, 4-phenylbutyric acid (PBA) partly alleviated the TG-induced ER stress. Moreover, TG inhibited HBsAg, HBeAg, and HBV DNA secretion from 12 to 48 h, while different concentrations of SA inhibited HBsAg and HBV DNA secretion at 48 h. TG promoted intracellular HBV DNA and HBsAg accumulation and the transcription of the HBV 3.5-kb mRNA and S mRNA. PBA treatment restored the secretion of HBsAg and HBV DNA. Finally, ER stress accelerated extracellular HBV DNA clearance but delayed intracellular HBV DNA clearance after ETV treatment.

Conclusions: Hepatocyte ER stress promoted intracellular HBV DNA and HBsAg accumulation by inhibiting their secretion. Our study also suggested that hepatocyte ER stress delayed intracellular HBV DNA clearance after ETV treatment.

Further evidence for the involvement of mitochondrial aquaporin-8 in hepatocyte lipid synthesis

We recently provided evidence suggesting that mitochondrial aquaporin-8 (mtAQP8), a channel protein able to conduct H₂O₂, is involved in the modulation of hepatocyte cholesterogenesis. To expand that study, we cultured human hepatocyte-derived Huh-7 cells in medium with lipoprotein-deficient serum (LPDS) to induce the de novo synthesis of cholesterol and fatty acids. We found that LPDS induced mtAQP8 expression and that AQP8 gene silencing significantly down-regulated the LPDS-induced synthesis of cholesterol and fatty acids as well as the expression of the corresponding key biosynthetic enzymes, 3-hydroxy-3-methylglutaryl-CoA reductase and fatty acid synthase. Our data further support a regulatory role of mtAQP8 in hepatocyte lipid homeostasis.

Orchestrated efforts on host network hijacking: Processes governing virus replication

With the high pervasiveness of viral diseases, the battle against viruses has never ceased. Here we discuss five cellular processes, namely "autophagy", "programmed cell death", "immune response", "cell cycle alteration", and "lipid metabolic reprogramming", that considerably guide viral replication after host infection in an orchestrated manner. On viral infection, "autophagy" and "programmed cell death" are two dynamically synchronized cell survival programs; "immune response" is a cell defense program typically suppressed by viruses; "cell cycle alteration" and "lipid metabolic reprogramming" are two altered cell housekeeping programs tunable in both directions. We emphasize on their functionalities in modulating viral replication, strategies viruses have evolved to tune these processes for their benefit, and how these processes orchestrate and govern cell fate upon viral infection. Understanding how viruses hijack host networks has both academic and industrial values in providing insights toward therapeutic strategy design for viral disease control, offering useful information in applications that aim to use viral vectors to improve human health such as gene therapy, and providing guidelines to maximize viral particle yield for improved vaccine production at a reduced cost.

The Clinically Approved Antifungal Drug Posaconazole Inhibits Human Cytomegalovirus Replication

Posaconazole (PCZ) is a clinically approved drug used predominantly for prophylaxis and salvage therapy of fungal infections. Here, we report its previously undescribed anti-human cytomegalovirus (HCMV) activity. By using antiviral assays, we demonstrated that PCZ, along with other azolic antifungals, has a broad anti-HCMV activity, being active against different strains, including low-passage-number clinical isolates and strains resistant to viral DNA polymerase inhibitors. Using a pharmacological approach, we identified the inhibition of human cytochrome P450 51 (hCYP51), or lanosterol 14α demethylase, a cellular target of posaconazole in infected cells, as a mechanism of anti-HCMV activity of the drug. Indeed, hCYP51 expression was stimulated upon HCMV infection, and the inhibition of its enzymatic activity by either the lanosterol analog VFV {(R)-N-(1-(3,4'-difluoro-[1,1'-biphenyl]-4-yl)-2-(1H-imidazol-1-yl)ethyl)-4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzamide} or PCZ decreased HCMV yield and infectivity of released virus particles. Importantly, we observed that the activity of the first-line anti-HCMV drug ganciclovir was boosted tenfold by PCZ and that ganciclovir (GCV) and PCZ act synergistically in inhibiting HCMV replication. Taken together, these findings suggest that this clinically approved drug deserves further investigation in the development of host-directed antiviral strategies as a candidate anti-HCMV drug with a dual antimicrobial effect.

Lipid-Assisted Membrane Protein Folding and Topogenesis

Due to the heterogenous lipid environment in which integral membrane proteins are embedded, they should follow a set of assembly rules, which govern transmembrane protein folding and topogenesis accordingly to a given lipid profile. Recombinant strains of bacteria have been engineered to have different membrane phospholipid compositions by molecular genetic manipulation of endogenous and foreign genes encoding lipid biosynthetic enzymes. Such strains provide a means to investigate the in vivo role of lipids in many different aspects of membrane function, folding and biogenesis. In vitro and in vivo studies established a function of lipids as molecular chaperones and topological determinants specifically assisting folding and topogenesis of membrane proteins. These results led to the extension of the Positive Inside Rule to Charge Balance Rule, which incorporates a role for lipid-protein interactions in determining membrane protein topological organization at the time of initial membrane insertion and dynamically after initial assembly. Membrane protein topogenesis appears to be a thermodynamically driven process in which lipid-protein interactions affect the potency of charged amino acid residues as topological signals. Dual topology for a membrane protein can be established during initial assembly where folding intermediates in multiple topological conformations are in rapid equilibrium (thus separated by a low activation energy), which is determined by the lipid environment. Post-assembly changes in lipid composition or post-translational modifications can trigger a reorganization of protein topology by inducing destabilization and refolding of a membrane protein. The lipid-dependent dynamic nature of membrane protein organization provides a novel means of regulating protein function.

Lipophilic Statins and Risk for Hepatocellular Carcinoma and Death in Patients With Chronic Viral Hepatitis: Results From a Nationwide Swedish Population

BACKGROUND

Whether statin type influences hepatocellular carcinoma (HCC) incidence or mortality in chronic hepatitis B or C virus infection is unknown.

OBJECTIVE

To assess the relationship between lipophilic or hydrophilic statin use and HCC incidence and mortality in a nationwide population with viral hepatitis.

DESIGN

Prospective propensity score (PS)-matched cohort.

SETTING

Swedish registers, 2005 to 2013.

PARTICIPANTS

A PS-matched cohort of 16 668 adults (8334 who initiated statin use [6554 lipophilic and 1780 hydrophilic] and 8334 nonusers) among 63 279 eligible adults.

MEASUREMENTS

Time to incident HCC, ascertained from validated registers. Statin use was defined from filled prescriptions as 30 or more cumulative defined daily doses (cDDDs).

RESULTS

Compared with matched nonusers, 10-year HCC risk was significantly lower among lipophilic statin users (8.1% vs. 3.3%; absolute risk difference [RD], -4.8 percentage points [95% CI, -6.2 to -3.3 percentage points]; adjusted subdistribution hazard ratio [aHR], 0.56 [CI, 0.41 to 0.79]) but not hydrophilic statin users (8.0% vs. 6.8%; RD, -1.2 percentage points [CI, -2.6 to 0.4 percentage points]; aHR, 0.95 [CI, 0.86 to 1.08]). The inverse association between lipophilic statins and HCC risk seemed to be dose-dependent. Compared with nonusers, 10-year HCC risk was lowest with 600 or more lipophilic statin cDDDs (8.4% vs. 2.5%; RD, -5.9 percentage points [CI, -7.6 to -4.2 percentage points]; aHR, 0.41 [CI, 0.32 to 0.61]), and 10-year mortality was significantly lower among both lipophilic (15.2% vs. 7.3%; RD, -7.9 percentage points [CI, -9.6 to -6.2 percentage points]) and hydrophilic (16.0% vs. 11.5%; RD, -4.5 percentage points [CI, -6.0 to -3.0 percentage points]) statin users.

LIMITATION

Lack of lipid, fibrosis, or HCC surveillance data.

CONCLUSION

In a nationwide viral hepatitis cohort, lipophilic statins were associated with significantly reduced HCC incidence and mortality. An association between hydrophilic statins and reduced risk for HCC was not found. Further research is needed to determine whether lipophilic statin therapy is feasible for prevention of HCC.

PRIMARY FUNDING SOURCE

None.

Oral administration of a chimeric Hepatitis B Virus S/preS1 antigen produced in lettuce triggers infection neutralizing antibodies in mice

Hepatitis B Virus (HBV) infection can be prevented by vaccination. Vaccines containing the small (S) envelope protein are currently used in universal vaccination programs and achieve protective immune response in more than 90% of recipients. However, new vaccination strategies are necessary for successful immunization of the remaining non- or low-responders. We have previously characterized a novel HBV chimeric antigen, which combines neutralization epitopes of the S and the preS1 domain of the large (L) envelope protein (genotype D). The S/preS121-47 chimera produced in mammalian cells and Nicotiana benthamiana plants, induced a significantly stronger immune response in parenterally vaccinated mice than the S protein. Here we describe the transient expression of the S/preS121-47 antigen in an edible plant, Lactuca sativa, for potential development of an oral HBV vaccine. Our study shows that oral administration of adjuvant-free Lactuca sativa expressing the S/preS121-47 antigen, three times, at 1 μg/dose, was sufficient to trigger a humoral immune response in mice. Importantly, the elicited antibodies were able to neutralize HBV infection in an NTCP-expressing infection system (HepG2-NTCP cell line) more efficiently than those induced by mice fed on Lactuca sativa expressing the S protein. These results support the S/preS121-47 antigen as a promising candidate for future development as an edible HBV vaccine.

A broad investigation of the HBV-mediated changes to primary hepatocyte physiology reveals HBV significantly alters metabolic pathways

OBJECTIVE

As the leading risk factor for the development of liver cancer, chronic infection with hepatitis B virus (HBV) represents a significant global health concern. Although an effective HBV vaccine exists, at least 240 million people are chronically infected with HBV worldwide. Therapeutic options for the treatment of chronic HBV remain limited, and none achieve an absolute cure. To develop novel therapeutic targets, a better understanding of the complex network of virus-host interactions is needed. Because of the central metabolic role of the liver, we assessed the metabolic impact of HBV infection as a means to identify viral dependency factors and metabolic pathways that could serve as novel points of therapeutic intervention.

METHODS

Primary rat hepatocytes were infected with a control adenovirus, an adenovirus expressing a greater-than-unit-length copy of the HBV genome, or an adenovirus expressing the HBV X protein (HBx). A panel of 369 metabolites was analyzed for HBV- or HBx-induced changes 24 and 48 h post infection. Pathway analysis was used to identify key metabolic pathways altered in the presence of HBV or HBx expression, and these findings were further supported through integration of publically available gene expression data.

RESULTS

We observed distinct changes to multiple metabolites in the context of HBV replication or HBx expression. Interestingly, a panel of 7 metabolites (maltotriose, maltose, myristate [14:0], arachidate [20:0], 3-hydroxybutyrate [BHBA], myo-inositol, and 2-palmitoylglycerol [16,0]) were altered by both HBV and HBx at both time points. In addition, incorporation of data from a transcriptome-based dataset allowed us to identify metabolic pathways, including long chain fatty acid metabolism, glycolysis, and glycogen metabolism, that were significantly altered by HBV and HBx.

CONCLUSIONS

Because the liver is a central regulator of metabolic processes, it is important to understand how HBV replication and HBV protein expression affects the metabolic function of hepatocytes. Through analysis of a broad panel of metabolites we investigated this metabolic impact. The results of these studies have defined metabolic consequences of an HBV infection of hepatocytes and will help to lay the groundwork for novel research directions and, potentially, development of novel anti-HBV therapeutics.

Silencing Retinoid X Receptor Alpha Expression Enhances Early-Stage Hepatitis B Virus Infection In Cell Cultures

Multiple steps of the life cycle of hepatitis B virus (HBV) are known to be coupled to hepatic metabolism. However, the details of involvement of the hepatic metabolic milieu in HBV infection remain incompletely understood. Hepatic lipid metabolism is controlled by a complicated transcription factor network centered on retinoid X receptor alpha (RXRα). Here, we report that RXRα negatively regulates HBV infection at an early stage in cell cultures. The RXR-specific agonist bexarotene inhibits HBV in HepG2 cells expressing the sodium taurocholate cotransporting polypeptide (NTCP) (HepG2-NTCP), HepaRG cells, and primary Tupaia hepatocytes (PTHs); reducing RXRα expression significantly enhanced HBV infection in the cells. Transcriptome sequencing (RNA-seq) analysis of HepG2-NTCP cells with a disrupted RXRα gene revealed that reduced gene expression in arachidonic acid (AA)/eicosanoid biosynthesis pathways, including the AA synthases phospholipase A2 group IIA (PLA2G2A), is associated with increased HBV infection. Moreover, exogenous treatment of AA inhibits HBV infection in HepG2-NTCP cells. These data demonstrate that RXRα is an important cellular factor in modulating HBV infection and implicate the participation of AA/eicosanoid biosynthesis pathways in the regulation of HBV infection.IMPORTANCE Understanding how HBV infection is connected with hepatic lipid metabolism may provide new insights into virus infection and its pathogenesis. By a series of genetic studies in combination with transcriptome analysis and pharmacological assays, we here investigated the role of cellular retinoid X receptor alpha (RXRα), a crucial transcription factor for controlling hepatic lipid metabolism, in de novo HBV infection in cell cultures. We found that silencing of RXRα resulted in elevated HBV covalently closed circular DNA (cccDNA) formation and viral antigen production, while activation of RXRα reduced HBV infection efficiency. Our results also showed that silencing phospholipase A2 group IIA (PLA2G2A), a key enzyme of arachidonic acid (AA) synthases, enhanced HBV infection efficiency in HepG2-NTCP cells and that exogenous AA treatment reduced de novo HBV infection in the cells. These findings unveil RXRα as an important cellular factor in modulating HBV infection and may point to a new strategy for host-targeted therapies against HBV.

A novel chimeric Hepatitis B virus S/preS1 antigen produced in mammalian and plant cells elicits stronger humoral and cellular immune response than the standard vaccine-constituent, S protein

Chronic Hepatitis B Virus (HBV) infection leads to severe liver pathogenesis associated with significant morbidity and mortality. As no curable medication is yet available, vaccination remains the most cost-effective approach to limit HBV spreading and control the infection. Although safe and efficient, the standard vaccine based on production of the small (S) envelope protein in yeast fails to elicit an effective immune response in about 10% of vaccinated individuals, which are at risk of infection. One strategy to address this issue is the development of more immunogenic antigens. Here we describe a novel HBV antigen obtained by combining relevant immunogenic determinants of S and large (L) envelope proteins. Our approach was based on the insertion of residues 21-47 of the preS1 domain of the L protein (nomenclature according to genotype D), involved in virus attachment to hepatocytes, within the external antigenic loop of S. The resulting S/preS121-47 chimera was successfully produced in HEK293T and Nicotiana benthamiana plants, as a more economical recombinant protein production platform. Comparative biochemical, functional and electron microscopy analysis indicated assembly of the novel antigen into subviral particles in mammalian and plant cells. Importantly, these particles preserve both S- and preS1-specific epitopes and elicit significantly stronger humoral and cellular immune responses than the S protein, in both expression systems used. Our data promote this antigen as a promising vaccine candidate to overcome poor responsiveness to the conventional, S protein-based, HBV vaccine.

Fatty acid translocase promoted hepatitis B virus replication by upregulating the levels of hepatic cytosolic calcium

Hepatitis B virus (HBV) is designated a "metabolovirus" due to the intimate connection between the virus and host metabolism. The nutrition state of the host plays a relevant role in the severity of HBV infection. Metabolic syndrome (MS) is prone to increasing HBV DNA loads and accelerating the progression of liver disease in patients with chronic hepatitis B (CHB). Cluster of differentiation 36 (CD36), also named fatty acid translocase, is known to facilitate long-chain fatty acid uptake and contribute to the development of MS. We recently found that CD36 overexpression enhanced HBV replication. In this study, we further explored the mechanism by which CD36 overexpression promotes HBV replication. Our data showed that CD36 overexpression increased HBV replication, and CD36 knockdown inhibited HBV replication. RNA sequencing found some of the differentially expressed genes were involved in calcium ion homeostasis. CD36 overexpression elevated the cytosolic calcium level, and CD36 knockdown decreased the cytosolic calcium level. Calcium chelator BAPTA-AM could override the HBV replication increased by CD36 overexpression, and the calcium activator thapsigargin could improve the HBV replication reduced by CD36 knockdown. We further found that CD36 overexpression activated Src kinase, which plays an important role in the regulation of the store-operated Ca²⁺ channel. An inhibitor of Src kinase (SU6656) significantly reduced the CD36-induced HBV replication. We identified a novel link between CD36 and HBV replication, which is associated with cytosolic calcium and the Src kinase pathway. CD36 may represent a potential therapeutic target for the treatment of CHB patients with MS.

Serum lipid profile as a marker of liver impairment in hepatitis B Cirrhosis patients

BACKGROUND

Chronic HBV infection is a major cause of Cirrhosis and an important risk factor to develop hepatocellular carcinoma. The study is conducted to find out the changes in the lipid metabolism of HBV-cirrhosis patients.

METHODS

In the present study, serum lipid profiles of patients with HBV-cirrhosis were assessed by utilizing micro-lab and gas chromatography, while risk factors for transmission of HBV-cirrhosis studied through the standard questionnaire.

RESULTS

The epidemiological and etiological risk factors strongly associated with HBV-cirrhosis patients compared to controls, included as family history, shave from the barber, blood transfusion (without proper screening), mutual sharing of household contents, positive surgery history, and dental treatment. The HBV-cirrhosis patients have significantly lower level (p < 0.001) of lipid profile including total cholesterol (96.65 mg/dl), TAG (82.85 mg/dl), VLDL-C (16.57 mg/dl), LDL-C (68.27 mg/dl), HDL-C (27 mg/dl) and total lipid (424.76 mg/dl) in comparison to controls, indicating hypolipidemia in patients. The MELD score indicated mild prognostic values of the hepatic function for the study group. The result of total fatty acid composition of HBV-cirrhotic patients with comparison of control subjects reveals that palmitic (24.54 g/100 g) and palmitoleic acid (4.65 g/100 g) were significantly (p < 0.05) higher whereas eicosatrienoic (0.09 g/100 g), arachidonic (3.57 g/100 g), linoleic (22.75 g/100 g) and α-linolenic acid (0.12 g/100 g) were significantly lower. Marker for stearoyl-CoA desaturase (SCD = ∆9-desaturase) activity i.e. palmitoleic: palmitic (0.2) and oleic: stearic acid (1.5) ratios, originated higher in HBV-cirrhotic patients, while PUFA: SFA (0.6) was lower in HBV-cirrhosis patients as compared with control subjects. The serum SFA and MUFA were increased while PUFA were reduced in both total and free form.

CONCLUSION

Present study concluded that hypolipidemia observed in HBV-cirrhosis patients, MELD were found to be independent predictors of survival and alteration in fatty acid composition, possibly due to impairment in fatty acid metabolism by enzymatic elongation and desaturation.

Effects of Interferons and Viruses on Metabolism

Interferons (IFNs) are potent pleiotropic cytokines that broadly alter cellular functions in response to viral and other infections. These alterations include changes in protein synthesis, proliferation, membrane composition, and the nutritional microenvironment. Recent evidence suggests that antiviral responses are supported by an IFN-induced rewiring of the cellular metabolism. In this review, we discuss the roles of type I and type II IFNs in regulating the cellular metabolism and biosynthetic reactions. Furthermore, we give an overview of how viruses themselves affect these metabolic activities to promote their replication. In addition, we focus on the lipid as well as amino acid metabolisms, through which IFNs exert potent antiviral and immunomodulatory activities. Conversely, the expression of IFNs is controlled by the nutrient sensor mammalian target of rapamycin or by direct reprograming of lipid metabolic pathways. These findings establish a mutual relationship between IFN production and metabolic core processes.

Transcriptome-Wide Analysis of Hepatitis B Virus-Mediated Changes to Normal Hepatocyte Gene Expression

Globally, a chronic hepatitis B virus (HBV) infection remains the leading cause of primary liver cancer. The mechanisms leading to the development of HBV-associated liver cancer remain incompletely understood. In part, this is because studies have been limited by the lack of effective model systems that are both readily available and mimic the cellular environment of a normal hepatocyte. Additionally, many studies have focused on single, specific factors or pathways that may be affected by HBV, without addressing cell physiology as a whole. Here, we apply RNA-seq technology to investigate transcriptome-wide, HBV-mediated changes in gene expression to identify single factors and pathways as well as networks of genes and pathways that are affected in the context of HBV replication. Importantly, these studies were conducted in an ex vivo model of cultured primary hepatocytes, allowing for the transcriptomic characterization of this model system and an investigation of early HBV-mediated effects in a biologically relevant context. We analyzed differential gene expression within the context of time-mediated gene-expression changes and show that in the context of HBV replication a number of genes and cellular pathways are altered, including those associated with metabolism, cell cycle regulation, and lipid biosynthesis. Multiple analysis pipelines, as well as qRT-PCR and an independent, replicate RNA-seq analysis, were used to identify and confirm differentially expressed genes. HBV-mediated alterations to the transcriptome that we identified likely represent early changes to hepatocytes following an HBV infection, suggesting potential targets for early therapeutic intervention. Overall, these studies have produced a valuable resource that can be used to expand our understanding of the complex network of host-virus interactions and the impact of HBV-mediated changes to normal hepatocyte physiology on viral replication.

The hepatitis B virus receptor

Hepatitis B virus (HBV) infection affects 240 million people worldwide. A liver-specific bile acid transporter named the sodium taurocholate cotransporting polypeptide (NTCP) has been identified as the cellular receptor for HBV and its satellite, the hepatitis D virus (HDV). NTCP likely acts as a major determinant for the liver tropism and species specificity of HBV and HDV at the entry level. NTCP-mediated HBV entry interferes with bile acid transport in cell cultures and has been linked with alterations in bile acid and cholesterol metabolism in vivo. The human liver carcinoma cell line HepG2, complemented with NTCP, now provides a valuable platform for studying the basic biology of the viruses and developing treatments for HBV infection. This review summarizes critical findings regarding NTCP's role as a viral receptor for HBV and HDV and discusses important questions that remain unanswered.

Statin use and risk of primary liver cancer in the Clinical Practice Research Datalink

BACKGROUND

Statins (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) are widely prescribed to reduce cholesterol levels. Studies have suggested that statins are associated with reduced risk of liver cancer, but much of the evidence is from regions of the world with high liver cancer incidence rates. The current study examined the statins-liver cancer relationship in a low-rate region and examined the effects of preexisting liver disease and diabetes on that association.

METHODS

A nested case-control study was conducted within the United Kingdom's Clinical Practice Research Datalink (CPRD). Persons diagnosed with primary liver cancer between 1988 and 2011 were matched to controls at a four-to-one ratio. Matches stratified on liver disease and on diabetes were also completed. Odds ratios (ORs) and 95% confidence intervals (CIs) for associations of statins with liver cancer were estimated using conditional logistic regression.

RESULTS

In total, 1195 persons with primary liver cancer were matched to 4640 control patients. Statin use was associated with a statistically significantly reduced risk of liver cancer (ORadj = 0.55, 95% CI = 0.45 to 0.69), especially among current users (ORadj = 0.53, 95% CI = 0.42 to 0.66). The reduced risk was statistically significant in the presence (ORadj = 0.32, 95% CI = 0.17 to 0.57) and absence of liver disease (ORadj = 0.65, 95% CI = 0.52 to 0.81) and in the presence (ORadj = 0.30, 95% CI = 0.21 to 0.42) and absence of diabetes (ORadj = 0.66, 95% CI = 0.51 to 0.85).

CONCLUSIONS

In the current study in a low-rate area, statin use was associated with a statistically significantly reduced risk of liver cancer overall. Risk was particularly reduced among persons with liver disease and persons with diabetes, suggesting that statin use may be especially beneficial in persons at elevated risk of liver cancer.

Binding of hepatitis B virus to its cellular receptor alters the expression profile of genes of bile acid metabolism

Chronic hepatitis B virus (HBV) infection has been associated with alterations in lipid metabolism. Moreover, the Na+-taurocholate cotransporting polypeptide (NTCP), responsible for bile acid (BA) uptake into hepatocytes, was identified as the functional cellular receptor mediating HBV entry. The aim of the study was to determine whether HBV alters the liver metabolic profile by employing HBV-infected and uninfected human liver chimeric mice. Humanized urokinase plasminogen activator/severe combined immunodeficiency mice were used to establish chronic HBV infection. Gene expression profiles were determined by real-time polymerase chain reaction using primers specifically recognizing transcripts of either human or murine origin. Liver biopsy samples obtained from HBV-chronic individuals were used to validate changes determined in mice. Besides modest changes in lipid metabolism, HBV-infected mice displayed a significant enhancement of human cholesterol 7α-hydroxylase (human [h]CYP7A1; median 12-fold induction; P<0.0001), the rate-limiting enzyme promoting the conversion of cholesterol to BAs, and of genes involved in transcriptional regulation, biosynthesis, and uptake of cholesterol (human sterol-regulatory element-binding protein 2, human 3-hydroxy-3-methylglutaryl-coenzyme A reductase, and human low-density lipoprotein receptor), compared to uninfected controls. Significant hCYP7A1 induction and reduction of human small heterodimer partner, the corepressor of hCYP7A1 transcription, was also confirmed in liver biopsies from HBV-infected patients. Notably, administration of Myrcludex-B, an entry inhibitor derived from the pre-S1 domain of the HBV envelope, provoked a comparable murine CYP7A1 induction in uninfected mice, thus designating the pre-S1 domain as the viral component triggering such metabolic alterations.

CONCLUSION

Binding of HBV to NTCP limits its function, thus promoting compensatory BA synthesis and cholesterol provision. The intimate link determined between HBV and liver metabolism underlines the importance to exploit further metabolic pathways, as well as possible NTCP-related viral-drug interactions.

Statin use and risk of hepatocellular carcinoma in a U.S. population

PURPOSE

Statins (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) are medications widely prescribed to reduce cholesterol levels. Observational studies in high-risk populations, mostly in Asia, have suggested that statins are associated with a reduced risk of hepatocellular carcinoma (HCC). The current study sought to evaluate the association of statin use and HCC in a U.S.-based, low-risk, general population.

METHODS

A nested case-control study was conducted among members of the Health Alliance Plan HMO of the Henry Ford Health System enrolled between 1999 and 2010. Electronic pharmacy records of statin use were compared among tumor registry-confirmed cases of HCC (n=94) and controls (n=468) matched on age, sex, diagnosis date, and length of HMO enrolment.

RESULTS

In multivariate analyses, ever-use of statins was significantly inversely associated with development of HCC (Odds ratio (OR): 0.32, 95%CI: 0.15-0.67). No clear dose-response relationship was evident as statin use for <2 years (OR=0.32, 95%CI=0.13-0.83) and >2 years (OR=0.31, 95CI%=0.12-9.81) resulted in very similar ORs.

CONCLUSIONS

The use of statins among populations in low-risk HCC areas may be associated with decreased risk of HCC.

Lipids and topological rules governing membrane protein assembly

Membrane protein folding and topogenesis are tuned to a given lipid profile since lipids and proteins have co-evolved to follow a set of interdependent rules governing final protein topological organization. Transmembrane domain (TMD) topology is determined via a dynamic process in which topogenic signals in the nascent protein are recognized and interpreted initially by the translocon followed by a given lipid profile in accordance with the Positive Inside Rule. The net zero charged phospholipid phosphatidylethanolamine and other neutral lipids dampen the translocation potential of negatively charged residues in favor of the cytoplasmic retention potential of positively charged residues (Charge Balance Rule). This explains why positively charged residues are more potent topological signals than negatively charged residues. Dynamic changes in orientation of TMDs during or after membrane insertion are attributed to non-sequential cooperative and collective lipid-protein charge interactions as well as long-term interactions within a protein. The proportion of dual topological conformers of a membrane protein varies in a dose responsive manner with changes in the membrane lipid composition not only in vivo but also in vitro and therefore is determined by the membrane lipid composition. Switching between two opposite TMD topologies can occur in either direction in vivo and also in liposomes (designated as fliposomes) independent of any other cellular factors. Such lipid-dependent post-insertional reversibility of TMD orientation indicates a thermodynamically driven process that can occur at any time and in any cell membrane driven by changes in the lipid composition. This dynamic view of protein topological organization influenced by the lipid environment reveals previously unrecognized possibilities for cellular regulation and understanding of disease states resulting from mis-folded proteins. This article is part of a Special Issue entitled: Protein trafficking and secretion in bacteria. Guest Editors: Anastassios Economou and Ross Dalbey.

Host-directed antimicrobial drugs with broad-spectrum efficacy against intracellular bacterial pathogens

We sought a new approach to treating infections by intracellular bacteria, namely, by altering host cell functions that support their growth. We screened a library of 640 Food and Drug Administration (FDA)-approved compounds for agents that render THP-1 cells resistant to infection by four intracellular pathogens. We identified numerous drugs that are not antibiotics but were highly effective in inhibiting intracellular bacterial growth with limited toxicity to host cells. These compounds are likely to target three kinds of host functions: (i) G protein-coupled receptors, (ii) intracellular calcium signals, and (iii) membrane cholesterol distribution. The compounds that targeted G protein receptor signaling and calcium fluxes broadly inhibited Coxiella burnetii, Legionella pneumophila, Brucella abortus, and Rickettsia conorii, while those directed against cholesterol traffic strongly attenuated the intracellular growth of C. burnetii and L. pneumophila. These pathways probably support intracellular pathogen growth so that drugs that perturb them may be therapeutic candidates. Combining host- and pathogen-directed treatments is a strategy to decrease the emergence of drug-resistant intracellular bacterial pathogens.

Although antibiotic treatment is often successful, it is becoming clear that alternatives to conventional pathogen-directed therapy must be developed in the face of increasing antibiotic resistance. Moreover, the costs and timing associated with the development of novel antimicrobials make repurposed FDA-approved drugs attractive host-targeted therapeutics. This paper describes a novel approach of identifying such host-targeted therapeutics against intracellular bacterial pathogens. We identified several FDA-approved drugs that inhibit the growth of intracellular bacteria, thereby implicating host intracellular pathways presumably utilized by bacteria during infection.

In vitro reconstitution of lipid-dependent dual topology and postassembly topological switching of a membrane protein

Phospholipids could exert their effect on membrane protein topology either directly by interacting with topogenic signals of newly inserted proteins or indirectly by influencing the protein assembly machinery. In vivo lactose permease (LacY) of Escherichia coli displays a mixture of topological conformations ranging from complete inversion of the N-terminal helical bundle to mixed topology and then to completely native topology as phosphatidylethanolamine (PE) is increased from 0% to 70% of membrane phospholipids. These topological conformers are interconvertible by postassembly synthesis or dilution of PE in vivo. To investigate whether coexistence of multiple topological conformers is dependent solely on the membrane lipid composition, we determined the topological organization of LacY in an in vitro proteoliposome system in which lipid composition can be systematically controlled before (liposomes) and after (fliposomes) reconstitution using a lipid exchange technique. Purified LacY reconstituted into preformed liposomes of increasing PE content displayed inverted topology at low PE and then a mixture of inverted and proper topologies with the latter increasing with increasing PE until all LacY adopted its native topology. Interconversion between topological conformers of LacY was observed in a PE dose-dependent manner by either increasing or decreasing PE levels in proteoliposomes postreconstitution of LacY, clearly demonstrating that membrane protein topology can be changed simply by changing membrane lipid composition independent of other cellular factors. The results provide a thermodynamic-based lipid-dependent model for shifting the equilibrium between different conformational states of a membrane protein.

Host factors involved in hepatitis B virus maturation, assembly, and egress

Hepatitis B virus (HBV) is a major cause of liver disease. Due to the tiny size of its genome, HBV depends on the critical interplay between viral and host factors for the generation of new viral particles from infected cells. Recent work has illuminated a multiplicity of spatially and temporally coordinated virus-host interactions that accompany HBV particle genesis. These interactions include the requirement of cellular chaperones for the maturation of the three viral envelope proteins, the cellular factors involved in dynamic modification, maturation, and intracellular trafficking of the nucleocapsids, and the host components of the multivesicular body (MVB) pathway enabling virion budding at intracellular compartments. Beside infectious virions, HBV produces at least two other types of particles, subviral empty envelope particles and subviral naked capsid particles, likely as a result of the engagement of different host factors by the viral structural proteins. Accordingly, HBV exploits distinct cellular pathways to release its particle types. Here, I review recent progress in these areas of the cell biology of HBV genesis.

Lipid-dependent generation of dual topology for a membrane protein

The mechanism by which membrane proteins exhibit structural and functional duality in the same membrane or different membranes is unknown. We posit that such duality is determined by both the protein sequence and the membrane lipid composition wherein a spatial or temporal change in the latter can result in a post-assembly change in protein structure and function. To investigate whether co-existence of multiple topological conformers is dependent on the membrane lipid composition, we determined the topological organization of lactose permease in an Escherichia coli model cell system in which phosphatidylethanolamine membrane content can be systematically varied. At intermediate levels of phosphatidylethanolamine a mixture of native and topologically mis-oriented conformers co-existed. There was no threshold level of phosphatidylethanolamine determining a sharp transition from one conformer to the other. Co-existing conformers were not in rapid equilibrium at a static lipid composition indicating that duality of topology is established during an early folding step. Depletion of intermediate levels of phosphatidylethanolamine after final protein assembly resulted in complete mis-orientation of the native conformer. Combined with previous results, such topological dynamics are reversible in both directions. We propose a thermodynamically based model for how lipid-protein interactions can result in a mixed topological organization and how changes in lipid composition can result in changes in the ratio of topologically distinct conformers of proteins. These observations demonstrate a potential lipid-dependent biological switch for generating dynamic structural and functional heterogeneity for a protein within the same membrane or between different membranes in more complex eukaryotic cells.

Entry of hepatitis B virus into immortalized human primary hepatocytes by clathrin-dependent endocytosis

The lack of a suitable in vitro hepatitis B virus (HBV) infectivity model has limited examination of the early stages of the virus-cell interaction. In this study, we used an immortalized cell line derived from human primary hepatocytes, HuS-E/2, to study the mechanism of HBV infection. HBV infection efficiency was markedly increased after dimethyl sulfoxide (DMSO)-induced differentiation of the cells. Transmission electron microscopy demonstrated the presence of intact HBV particles in DMSO-treated HBV-infected HuS-E/2 cells, which could be infected with HBV for up to at least 50 passages. The pre-S1 domain of the large HBsAg (LHBsAg) protein specifically interacted with clathrin heavy chain (CHC) and clathrin adaptor protein AP-2. Short hairpin RNA knockdown of CHC or AP-2 in HuS-E/2 cells significantly reduced their susceptibility to HBV, indicating that both are necessary for HBV infection. Furthermore, HBV entry was inhibited by chlorpromazine, an inhibitor of clathrin-mediated endocytosis. LHBsAg also interfered with the clathrin-mediated endocytosis of transferrin by human hepatocytes. This infection system using an immortalized human primary hepatocyte cell line will facilitate investigations into HBV entry and in devising therapeutic strategies for manipulating HBV-associated liver disorders.