Association between hepatitis C virus and very-low-density lipoprotein (VLDL)/LDL analyzed in iodixanol density gradients

Host-targeting antivirals for chronic viral infections of the liver

Infection with one or several of the five known hepatitis viruses is a leading cause of liver disease and poses a high risk of developing hepatocellular carcinoma upon chronic infection. Chronicity is primarily caused by hepatitis B virus (HBV) and hepatitis C virus (HCV) and poses a significant health burden worldwide. Co-infection of chronic HBV infected patients with hepatitis D virus (HDV) is less common but is marked as the most severe form of chronic viral hepatitis. Hepatitis A virus (HAV) and hepatitis E virus (HEV) primarily cause self-limiting acute hepatitis. However, studies have also reported chronic progression of HEV disease in immunocompromised patients. While considerable progress has been made in the treatment of HCV and HBV through the development of direct-acting antivirals (DAAs), challenges including drug resistance, incomplete viral suppression resulting in failure to achieve clearance and the lack of effective treatment options for HDV and HEV remain. Host-targeting antivirals (HTAs) have emerged as a promising alternative approach to DAAs and aim to disrupt virus-host interactions by modulating host cell pathways that are hijacked during the viral replication cycle. The aim of this review is to provide a comprehensive overview about the major milestones in research and development of HTAs for chronic HBV/HDV and HCV infections. It also summarizes the current state of knowledge on promising host-targeting therapeutic options against HEV infection.

Hepatitis C virus E1 recruits high-density lipoprotein to support infectivity and evade antibody recognition

Hepatitis C virus (HCV) is a member of the Flaviviridae family; however, unlike other family members, the HCV virion has an unusually high lipid content. HCV has two envelope glycoproteins, E1 and E2. E2 contributes to receptor binding, cell membrane attachment, and immune evasion. In contrast, the functions of E1 are poorly characterized due, in part, to challenges in producing the protein. This manuscript describes the expression and purification of a soluble E1 ectodomain (eE1) that is recognized by conformational, human monoclonal antibodies. eE1 forms a complex with apolipoproteins AI and AII, cholesterol, and phospholipids by recruiting high-density lipoprotein (HDL) from the extracellular media. We show that HDL binding is a function specific to eE1 and HDL hinders recognition of E1 by a neutralizing monoclonal antibody. Either low-density lipoprotein or HDL increases the production and infectivity of cell culture-produced HCV, but E1 preferentially selects HDL, influencing both viral life cycle and antibody evasion.IMPORTANCEHepatitis C virus (HCV) infection is a significant burden on human health, but vaccine candidates have yet to provide broad protection against this infection. We have developed a method to produce high quantities of soluble E1 or E2, the viral proteins located on the surface of HCV. HCV has an unusually high lipid content due to the recruitment of apolipoproteins. We found that E1 (and not E2) preferentially recruits host high-density lipoprotein (HDL) extracellularly. This recruitment of HDL by E1 prevents binding of E1 by a neutralizing antibody and furthermore prevents antibody-mediated neutralization of the virus. By comparison, low-density lipoprotein does not protect the virus from antibody-mediated neutralization. Our findings provide mechanistic insight into apolipoprotein recruitment, which may be critical for vaccine development.

The interplay between lipid droplets and virus infection

As an intracellular parasite, the virus usurps cellular machinery and modulates cellular metabolism pathways to replicate itself in cells. Lipid droplets (LDs) are universally conserved energy storage organelles that not only play vital roles in maintaining lipid homeostasis but are also involved in viral replication. Increasing evidence has demonstrated that viruses take advantage of cellular lipid metabolism by targeting the biogenesis, hydrolysis, and lipophagy of LD during viral infection. In this review, we summarize the current knowledge about the modulation of cellular LD by different viruses, with a special emphasis on the Hepatitis C virus, Dengue virus, and SARS-CoV-2.

Recruitment of Receptors and Ligands in a Weakly Multivalent System with Omnipresent Signatures of Superselective Binding

Recruitment of receptors at membrane interfaces is essential in biological recognition and uptake processes. The interactions that induce recruitment are typically weak at the level of individual interaction pairs, but are strong and selective at the level of recruited ensembles. Here, a model system is demonstrated, based on the supported lipid bilayer (SLB) that mimics the recruitment process induced by weakly multivalent interactions. The weak (mm range) histidine-nickel-nitrilotriacetate (His₂ -NiNTA) pair is employed owing to its ease of implementation in both synthetic and biological systems. The recruitment of receptors (and ligands) induced by the binding of His₂ -functionalized vesicles on NiNTA-terminated SLBs is investigated to identify the ligand densities necessary to achieve vesicle binding and receptor recruitment. Threshold values of ligand densities appear to occur in many binding characteristics: density of bound vesicles, size and receptor density of the contact area, and vesicle deformation. Such thresholds contrast the binding of strongly multivalent systems and constitute a clear signature of the superselective binding behavior predicted for weakly multivalent interactions. This model system provides quantitative insight into the binding valency and effects of competing energetic forces, such as deformation, depletion, and entropy cost of recruitment at different length scales.

The role of human lipoproteins for hepatitis C virus persistence

Hepatitis C virus (HCV) is a hepatotropic virus that establishes a chronic infection in most individuals. Effective treatments are available; however, many patients are not aware of their infection. Consequently, they do not receive treatment and HCV transmission remains high, particularly among groups at high risk of exposure such as people who inject intravenous drugs. A prophylactic vaccine may reduce HCV transmission, but is currently not available. HCV has evolved immune evasion strategies, which facilitate persistence and complicate development of a protective vaccine. The peculiar association of HCV particles with human lipoproteins is thought to facilitate evasion from humoral immune response and viral homing to liver cells. A better understanding of these aspects provides the basis for development of protective vaccination strategies. Here, we review key information about the composition of HCV particles, the mechanisms mediating lipoprotein incorporation, and the functional consequences of this interaction.

The Role of Cytosolic Lipid Droplets in Hepatitis C Virus Replication, Assembly, and Release

The hepatitis C virus (HCV) causes chronic hepatitis by establishing a persistent infection. Patients with chronic hepatitis frequently develop hepatic cirrhosis, which can lead to liver cancer-the progressive liver damage results from the host's immune response to the unresolved infection. The HCV replication process, including the entry, replication, assembly, and release stages, while the virus circulates in the bloodstream, it is intricately linked to the host's lipid metabolism, including the dynamic of the cytosolic lipid droplets (cLDs). This review article depicts how this interaction regulates viral cell tropism and aids immune evasion by coining viral particle characteristics. cLDs are intracellular organelles that store most of the cytoplasmic components of neutral lipids and are assumed to play an increasingly important role in the pathophysiology of lipid metabolism and host-virus interactions. cLDs are involved in the replication of several clinically significant viruses, where viruses alter the lipidomic profiles of host cells to improve viral life cycles. cLDs are involved in almost every phase of the HCV life cycle. Indeed, pharmacological modulators of cholesterol synthesis and intracellular trafficking, lipoprotein maturation, and lipid signaling molecules inhibit the assembly of HCV virions. Likewise, small-molecule inhibitors of cLD-regulating proteins inhibit HCV replication. Thus, addressing the molecular architecture of HCV replication will aid in elucidating its pathogenesis and devising preventive interventions that impede persistent infection and prevent disease progression. This is possible via repurposing the available therapeutic agents that alter cLDs metabolism. This review highlights the role of cLD in HCV replication.

What role for cellular metabolism in the control of hepatitis viruses?

Hepatitis B, C and D viruses (HBV, HCV, HDV, respectively) specifically infect human hepatocytes and often establish chronic viral infections of the liver, thus escaping antiviral immunity for years. Like other viruses, hepatitis viruses rely on the cellular machinery to meet their energy and metabolite requirements for replication. Although this was initially considered passive parasitism, studies have shown that hepatitis viruses actively rewire cellular metabolism through molecular interactions with specific enzymes such as glucokinase, the first rate-limiting enzyme of glycolysis. As part of research efforts in the field of immunometabolism, it has also been shown that metabolic changes induced by viruses could have a direct impact on the innate antiviral response. Conversely, detection of viral components by innate immunity receptors not only triggers the activation of the antiviral defense but also induces in-depth metabolic reprogramming that is essential to support immunological functions. Altogether, these complex triangular interactions between viral components, innate immunity and hepatocyte metabolism may explain why chronic hepatitis infections progressively lead to liver inflammation and progression to cirrhosis, fibrosis and hepatocellular carcinoma (HCC). In this manuscript, we first present a global overview of known connections between the innate antiviral response and cellular metabolism. We then report known molecular mechanisms by which hepatitis viruses interfere with cellular metabolism in hepatocytes and discuss potential consequences on the innate immune response. Finally, we present evidence that drugs targeting hepatocyte metabolism could be used as an innovative strategy not only to deprive viruses of key metabolites, but also to restore the innate antiviral response that is necessary to clear infection.

Neutralization and receptor use of infectious culture-derived rat hepacivirus as a model for HCV

BACKGROUND AND AIMS

Lack of tractable immunocompetent animal models amenable to robust experimental challenge impedes vaccine efforts for HCV. Infection with rodent hepacivirus from Rattus norvegicus (RHV-rn1) in rats shares HCV-defining characteristics, including liver tropism, chronicity, and pathology. RHV in vitro cultivation would facilitate genetic studies on particle production, host factor interactions, and evaluation of antibody neutralization guiding HCV vaccine approaches.

APPROACH AND RESULTS

We report an infectious reverse genetic cell culture system for RHV-rn1 using highly permissive rat hepatoma cells and adaptive mutations in the E2, NS4B, and NS5A viral proteins. Cell culture-derived RHV-rn1 particles (RHVcc) share hallmark biophysical characteristics of HCV and are infectious in mice and rats. Culture adaptive mutations attenuated RHVcc in immunocompetent rats, and the mutations reverted following prolonged infection, but not in severe combined immunodeficiency (SCID) mice, suggesting that adaptive immune pressure is a primary driver of reversion. Accordingly, sera from RHVcc-infected SCID mice or the early acute phase of immunocompetent mice and rats were infectious in culture. We further established an in vitro RHVcc neutralization assay, and observed neutralizing activity of rat sera specifically from the chronic phase of infection. Finally, we found that scavenger receptor class B type I promoted RHV-rn1 entry in vitro and in vivo.

CONCLUSIONS

The RHV-rn1 infectious cell culture system enables studies of humoral immune responses against hepacivirus infection. Moreover, recapitulation of the entire RHV-rn1 infectious cycle in cell culture will facilitate reverse genetic studies and the exploration of tropism and virus-host interactions.

Emerging Evidence of Pathological Roles of Very-Low-Density Lipoprotein (VLDL)

Embraced with apolipoproteins (Apo) B and Apo E, triglyceride-enriched very-low-density lipoprotein (VLDL) is secreted by the liver into circulation, mainly during post-meal hours. Here, we present a brief review of the physiological role of VLDL and a systemic review of the emerging evidence supporting its pathological roles. VLDL promotes atherosclerosis in metabolic syndrome (MetS). VLDL isolated from subjects with MetS exhibits cytotoxicity to atrial myocytes, induces atrial myopathy, and promotes vulnerability to atrial fibrillation. VLDL levels are affected by a number of endocrinological disorders and can be increased by therapeutic supplementation with cortisol, growth hormone, progesterone, and estrogen. VLDL promotes aldosterone secretion, which contributes to hypertension. VLDL induces neuroinflammation, leading to cognitive dysfunction. VLDL levels are also correlated with chronic kidney disease, autoimmune disorders, and some dermatological diseases. The extra-hepatic secretion of VLDL derived from intestinal dysbiosis is suggested to be harmful. Emerging evidence suggests disturbed VLDL metabolism in sleep disorders and in cancer development and progression. In addition to VLDL, the VLDL receptor (VLDLR) may affect both VLDL metabolism and carcinogenesis. Overall, emerging evidence supports the pathological roles of VLDL in multi-organ diseases. To better understand the fundamental mechanisms of how VLDL promotes disease development, elucidation of the quality control of VLDL and of the regulation and signaling of VLDLR should be indispensable. With this, successful VLDL-targeted therapies can be discovered in the future.

Differentiated Cells in Prolonged Hypoxia Produce Highly Infectious Native-Like Hepatitis C Virus Particles

BACKGROUND AND AIMS

Standard hepatitis C virus (HCV) cell-culture models present an altered lipid metabolism and thus produce lipid-poor lipoviral particles (LVPs). These models are thereby weakly adapted to explore the complete natural viral life cycle.

APPROACH AND RESULTS

To overcome these limitations, we used an HCV cell-culture model based on both cellular differentiation and sustained hypoxia to better mimic the host-cell environment. The long-term exposure of Huh7.5 cells to DMSO and hypoxia (1% O₂ ) significantly enhanced the expression of major differentiation markers and the cellular hypoxia adaptive response by contrast with undifferentiated and normoxic (21% O₂ ) standard conditions. Because hepatocyte-like differentiation and hypoxia are key regulators of intracellular lipid metabolism, we characterized the distribution of lipid droplets (LDs) and demonstrated that experimental cells significantly accumulate larger and more numerous LDs relative to standard cell-culture conditions. An immunocapture (IC) and transmission electron microscopy (TEM) method showed that differentiated and hypoxic Huh7.5 cells produced lipoproteins significantly larger than those produced by standard Huh7.5 cell cultures. The experimental cell culture model is permissive to HCV-Japanese fulminant hepatitis (JFH1) infection and produces very-low-buoyant-density LVPs that are 6-fold more infectious than LVPs formed by standard JFH1-infected Huh7.5 cells. Finally, the IC-TEM approach and antibody-neutralization experiments revealed that LVPs were highly lipidated, had a global ultrastructure and a conformation of the envelope glycoprotein complex E1E2 close to that of the ones circulating in infected individuals.

CONCLUSIONS

This relevant HCV cell culture model thus mimics the complete native intracellular HCV life cycle and, by extension, can be proposed as a model of choice for studies of other hepatotropic viruses.

Glycometabolism regulates hepatitis C virus release

HCV cell-culture system uses hepatoma-derived cell lines for efficient virus propagation. Tumor cells cultured in glucose undergo active aerobic glycolysis, but switch to oxidative phosphorylation for energy production when cultured in galactose. Here, we investigated whether modulation of glycolysis in hepatocytes affects HCV infection. We showed HCV release, but not entry, genome replication or virion assembly, is significantly blocked when cells are cultured in galactose, leading to accumulation of intracellular infectious virions within multivesicular body (MVB). Blockade of the MVB-lysosome fusion or treatment with pro-inflammatory cytokines promotes HCV release in galactose. Furthermore, we found this glycometabolic regulation of HCV release is mediated by MAPK-p38 phosphorylation. Finally, we showed HCV cell-to-cell transmission is not affected by glycometabolism, suggesting that HCV cell-to-supernatant release and cell-to-cell transmission are two mechanistically distinct pathways. In summary, we demonstrated glycometabolism regulates the efficiency and route of HCV release. We proposed HCV may exploit the metabolic state in hepatocytes to favor its spread through the cell-to-cell transmission in vivo to evade immune response.

Hepatitis C virus (HCV) is a positive-stranded RNA virus that causes acute and chronic hepatitis and hepatocellular carcinoma. HCV infectious cycle comprises viral entry, uncoating, translation and replication of viral RNA, assembly into new virions and release. Establishment of HCV cell culture system (HCVcc) has yielded many insights into complete HCV infectious cycle in Huh7 cell and Huh7-derived human hepatoma cell lines. However, because hepatoma-derived cell lines and hepatocytes vary in metabolism, HCV infectious cycle in tumor cell lines and the patient’s liver may also be different. Therefore, we explored the alterations of HCV infectious cycle by forcing the tumor cell lines to switch their glycometabolic pathways. We found that HCV release can be blocked by culturing cells in galactose-containing medium, leading to accumulation of intracellular infectious virions within MVB. Moreover, we provided new evidence to suggest that HCV cell-to-cell transmission may be mechanistically distinct from cell-to-supernatant release. Finally, we proposed a new concept that HCV release from hepatocytes into circulation may be naturally inefficient due to the metabolic state in liver that may favor more HCV cell-to-cell transmission. This strategy would allow HCV to effectively evade neutralizing antibodies to establish persistent infection.

Hepatitis C Virus Uses Host Lipids to Its Own Advantage

Lipids and lipoproteins constitute indispensable components for living not only for humans. In the case of hepatitis C virus (HCV), the option of using the products of our lipid metabolism is “to be, or not to be”. On the other hand, HCV infection, which is the main cause of chronic hepatitis, cirrhosis and hepatocellular carcinoma, exerts a profound influence on lipid and lipoprotein metabolism of the host. The consequences of this alternation are frequently observed as hypolipidemia and hepatic steatosis in chronic hepatitis C (CHC) patients. The clinical relevance of these changes reflects the fact that lipids and lipoprotein play a crucial role in all steps of the life cycle of HCV. The virus circulates in the bloodstream as a highly lipidated lipo-viral particle (LVP) that defines HCV hepatotropism. Thus, strict relationships between lipids/lipoproteins and HCV are indispensable for the mechanism of viral entry into hepatocytes, viral replication, viral particles assembly and secretion. The purpose of this review is to summarize the tricks thanks to which HCV utilizes host lipid metabolism to its own advantage.

Impact of DAA-Based Regimens on HCV-Related Extra-Hepatic Damage: A Narrative Review

Two-third of patients with chronic hepatitis C show extrahepatic manifestations due to HCV infection of B lymphocytes, such as mixed cryoglobulinemia and non-Hodgkin B-cell lymphoma, or develop a chronic inflammatory status that may favor the development of adverse cardiovascular events, kidney diseases or metabolic abnormalities.DAAs treatments induce HCV eradication in 95% of treated patients, which also improves the clinical course of extrahepatic manifestations, but with some limitations. After HCV eradication a good compensation of T2DM has been observed, but doubts persist about the possibility of obtaining a stable reduction in fasting glucose and HbA1c levels.Chronic HCV infection is associated with low total and LDL cholesterol serum levels, which however increase significantly after HCV elimination, possibly due to the disruption of HCV/lipid metabolism interaction. Despite this adverse effect, HCV eradication exerts a favorable action on cardiovascular system, possibly by eliminating numerous other harmful effects exerted by HCV on this system.DAA treatment is also indicated for the treatment of patients with mixed cryoglobulinemia syndrome, since HCV eradication results in symptom reduction and, in particular, is effective in cryoglobulinemic vasculitis. Furthermore, HCV eradication exerts a favorable action on HCV-related lymphoproliferative disorders, with frequent remission or reduction of clinical manifestations.There is also evidence that HCV clearance may improve impaired renal functions, but same conflicting data persist on the effect of some DAAs on eGFR.

Adaptive mutations promote hepatitis C virus assembly by accelerating core translocation to the endoplasmic reticulum

The envelopment of hepatitis C virus (HCV) is believed to occur primarily in the endoplasmic reticulum (ER)-associated membrane, and the translocation of viral Core protein from lipid droplets (LDs) to the ER is essential for the envelopment of viral particles. However, the factors involved are not completely understood. Herein, we identified eight adaptive mutations that enhanced virus spread and infectivity of genotype 1a clone TNcc in hepatoma Huh7 cells through long-term culture adaptation and reverse genetic study. Of eight mutations, I853V in NS2 and C2865F in NS5B were found to be minimal mutation sets that enabled an increase in virus production without apparently affecting RNA replication, thus suggesting its roles in the post-replication stage of the HCV life cycle. Using a protease K protection and confocal microscopy analysis, we demonstrated that C2865F and the combination of I853V/C2865F enhanced virus envelopment by facilitating Core translocation from the LDs to the ER. Buoyant density analysis revealed that I853V/C2865F contributed to the release of virion with a density of ∼1.10 g/ml. Moreover, we demonstrated that NS5B directly interacted with NS2 at the protease domain and that mutations I853V, C2865F, and I853V/C2865F enhanced the interaction. In addition, C2865F also enhanced the interaction between NS5B and Core. In conclusion, this study demonstrated that adaptive mutations in NS2 and NS5B promoted HCV envelopment by accelerating Core translocation from the LDs to the ER and reinforced the interaction between NS2 and NS5B. The findings facilitate our understanding of the assembly of HCV morphogenesis.

HCV Assembly and Egress via Modifications in Host Lipid Metabolic Systems

Hepatitis C virus (HCV) proliferates by hijacking the host lipid machinery. In vitro replication systems revealed many aspects of the virus life cycle; in particular, viral utilization of host lipid metabolism during HCV proliferation. HCV interacts with lipid droplets (LDs) before starting the process of virus capsid formation at the lipid-rich endoplasmic reticulum (ER) membrane compartment. HCV buds into the ER via lipoprotein assembly and secretion. Exchangeable apolipoproteins, represented by apolipoprotein E (apoE), play pivotal roles in enhancing HCV-specific infectivity. HCV virions are likely to interact with other lipoproteins circulating in blood vessels and incorporate apolipoproteins as well as lipids. This review focuses on virus assembly and egress by briefly describing the recent advances in this area.

Delayed by Design: Role of Suboptimal Signal Peptidase Processing of Viral Structural Protein Precursors in Flaviviridae Virus Assembly

The Flaviviridae virus family is classified into four different genera, including flavivirus, hepacivirus, pegivirus, and pestivirus, which cause significant morbidity and mortality in humans and other mammals, including ruminants and pigs. These are enveloped, single-stranded RNA viruses sharing a similar genome organization and replication scheme with certain unique features that differentiate them. All viruses in this family express a single polyprotein that encodes structural and nonstructural proteins at the N- and C-terminal regions, respectively. In general, the host signal peptidase cleaves the structural protein junction sites, while virus-encoded proteases process the nonstructural polyprotein region. It is known that signal peptidase processing is a rapid, co-translational event. Interestingly, certain signal peptidase processing site(s) in different Flaviviridae viral structural protein precursors display suboptimal cleavage kinetics. This review focuses on the recent progress regarding the Flaviviridae virus genus-specific mechanisms to downregulate signal peptidase-mediated processing at particular viral polyprotein junction sites and the role of delayed processing at these sites in infectious virus particle assembly.

HCV Interplay with Lipoproteins: Inside or Outside the Cells?

Hepatitis C virus (HCV) infection is a major public health issue leading to chronic liver diseases. HCV particles are unique owing to their particular lipid composition, namely the incorporation of neutral lipids and apolipoproteins. The mechanism of association between HCV virion components and these lipoproteins factors remains poorly understood as well as its impact in subsequent steps of the viral life cycle, such as entry into cells. It was proposed that the lipoprotein biogenesis pathway is involved in HCV morphogenesis; yet, recent evidence indicated that HCV particles can mature and evolve biochemically in the extracellular medium after egress. In addition, several viral, cellular and blood components have been shown to influence and regulate this specific association. Finally, this specific structure and composition of HCV particles was found to influence entry into cells as well as their stability and sensitivity to neutralizing antibodies. Due to its specific particle composition, studying the association of HCV particles with lipoproteins remains an important goal towards the rational design of a protective vaccine.

Hepatitis C Virus Entry: An Intriguingly Complex and Highly Regulated Process

Hepatitis C virus (HCV) is a major cause of chronic hepatitis and liver disease worldwide. Its tissue and species tropism are largely defined by the viral entry process that is required for subsequent productive viral infection and establishment of chronic infection. This review provides an overview of the viral and host factors involved in HCV entry into hepatocytes, summarizes our understanding of the molecular mechanisms governing this process and highlights the therapeutic potential of host-targeting entry inhibitors.

Apolipoprotein M, identified as a novel hepatitis C virus (HCV) particle associated protein, contributes to HCV assembly and interacts with E2 protein

Hepatitis C virus (HCV) infection is a major cause of chronic liver diseases such as steatosis, cirrhosis, and hepatocellular carcinoma. HCV particles have been found to associate with apolipoproteins, and apolipoproteins not only participate in the HCV life cycle, but also help HCV escape recognition by the host immune system, which pose challenges for the development of both HCV treatments and vaccines. However, no study has reported on the comprehensive identification of apolipoprotein associations with HCV particles. In the present study, we performed proteome analysis by affinity purification coupled with mass spectrometry (AP-MS) to comprehensively identify the apolipoprotein associations with HCV particles, and ApoM was first identified by AP-MS besides the previously reported ApoE, ApoB, ApoA-I and ApoC-I. Additionally, three assays further confirmed that ApoM was a novel virus particle associated protein. We also showed that ApoM was required for HCV production, especially for the assembly/release step of HCV life cycle. Furthermore, ApoM interacted with the HCV E2 protein. Finally, HCV infection reduced ApoM expression both in vitro and in vivo. Collectively, our study demonstrates that ApoM, identified as a novel HCV particle associated protein, contributes to HCV assembly/release and interacts with HCV E2 protein. It provides new insights on how HCV and the host apolipoproteins are reciprocally influenced and lays a basis for research in developing innovative antiviral strategies.

Long-chain fatty acyl-coenzyme A suppresses hepatitis C virus infection by targeting virion-bound lipoproteins

Hepatitis C virus (HCV) is a leading cause of chronic hepatitis and end-stage liver diseases. Mature HCV virions are bound by host-derived lipoproteins. Lack of an HCV vaccine warrants a major role of antiviral treatment in the global elimination of hepatitis C. Although direct-acting antivirals (DAAs) are replacing the interferon-based treatment and have dramatically improved the cure rate, the presence of viral variants resistant to DAAs, HCV genotype/subtype-specific efficacy, and high cost of DAAs argue novel and affordable regimens. In this study, we identified the antiviral effects of long-chain fatty acyl-coenzyme A (LCFA-CoA) against the infections of HCV genotypes 1-6 through targeting mature HCV-bound lipoproteins, suggesting novel mechanism(s) of antiviral different from those used by host-targeting agents or DAAs. We found that the antiviral activity of LCFA-CoA relied on the long-chain saturated fatty acid and the CoA group, and was enhanced when combined with pegylated-interferon or DAAs. Importantly, we demonstrated that LCFA-CoA efficiently inhibited the infection of HCV variants carrying DAA-resistant mutations. The mechanistic study revealed that LCFA-CoA specifically abolished the attachment and binding steps and also inhibited the cell-to-cell viral transmission. LCFA-CoA targeted mature HCV-bound lipoproteins, but not apolipoproteins B or E. In addition, LCFA-CoA could also inhibit the infection of the dengue virus. Our findings suggest that LCFA-CoA could potentially serve as a supplement HCV therapy, particularly for the DAA-resistant HCV variants. Taken together, LCFA-CoA may be further developed to be a novel class of antivirals with mechanism(s), different from host-targeting agents or DAAs, of targeting the components associated with mature HCV virions.

Roles of secretory glycoproteins in particle formation of Flaviviridae viruses

The family Flaviviridae comprises four genera, namely, Flavivirus, Pestivirus, Pegivirus, and Hepacivirus. These viruses have similar genome structures, but the genomes of Pestivirus and Flavivirus encode the secretory glycoproteins E^rns and NS1, respectively. E^rns plays an important role in virus particle formation and cell entry, whereas NS1 participates in the formation of replication complexes and virus particles. Conversely, apolipoproteins are known to participate in the formation of infectious particles of hepatitis C virus (HCV) and various secretory glycoproteins play a similar role in HCV particles formation, suggesting that there is no strong specificity for the function of secretory glycoproteins in infectious-particle formation. In addition, recent studies have shown that host-derived apolipoproteins and virus-derived E^rns and NS1 play comparable roles in infectious-particle formation of both HCV and pestiviruses. In this review, we summarize the roles of secretory glycoproteins in the formation of Flaviviridae virus particles.

A serum protein factor mediates maturation and apoB-association of HCV particles in the extracellular milieu

BACKGROUND & AIMS

In the sera of infected patients, hepatitis C virus (HCV) particles display heterogeneous forms with low-buoyant densities (<1.08), underscoring their lipidation via association with apoB-containing lipoproteins, which was proposed to occur during assembly or secretion from infected hepatocytes. However, the mechanisms inducing this association remain poorly-defined and most cell culture grown HCV (HCVcc) particles exhibit higher density (>1.08) and poor/no association with apoB. We aimed to elucidate the mechanisms of lipidation and to produce HCVcc particles resembling those in infected sera.

METHODS

We produced HCVcc particles of Jc1 or H77 strains from Huh-7.5 hepatoma cells cultured in standard conditions (10%-fetal calf serum) vs. in serum-free or human serum conditions before comparing their density profiles to patient-derived virus. We also characterized wild-type and Jc1/H77 hypervariable region 1 (HVR1)-swapped mutant HCVcc particles produced in serum-free media and incubated with different serum types or with purified lipoproteins.

RESULTS

Compared to serum-free or fetal calf serum conditions, production with human serum redistributed most HCVcc infectious particles to low density (<1.08) or very-low density (<1.04) ranges. In addition, short-time incubation with human serum was sufficient to shift HCVcc physical particles to low-density fractions, in time- and dose-dependent manners, which increased their specific infectivity, promoted apoB-association and induced neutralization-resistance. Moreover, compared to Jc1, we detected higher levels of H77 HCVcc infectious particles in very-low-density fractions, which could unambiguously be attributed to strain-specific features of the HVR1 sequence. Finally, all 3 lipoprotein classes, i.e., very-low-density, low-density and high-density lipoproteins, could synergistically induce low-density shift of HCV particles; yet, this required additional non-lipid serum factor(s) that include albumin.

CONCLUSIONS

The association of HCV particles with lipids may occur in the extracellular milieu. The lipidation level depends on serum composition as well as on HVR1-specific properties. These simple culture conditions allow production of infectious HCV particles resembling those of chronically-infected patients.

LAY SUMMARY

Hepatitis C virus (HCV) particles may associate with apoB and acquire neutral lipids after exiting cells, giving them low-buoyant density. The hypervariable region 1 (HVR1) is a majorviral determinant of E2 that controls this process. Besides lipoproteins, specific serum factors including albumin promote extracellular maturation of HCV virions. HCV particle production in vitro, with media of defined serum conditions, enables production of infectious particles resembling those of chronically infected patients.

HCV Pit Stop at the Lipid Droplet: Refuel Lipids and Put on a Lipoprotein Coat before Exit

The replication cycle of the liver-tropic hepatitis C virus (HCV) is tightly connected to the host lipid metabolism, during the virus entry, replication, assembly and egress stages, but also while the virus circulates in the bloodstream. This interplay coins viral particle properties, governs viral cell tropism, and facilitates immune evasion. This review summarizes our knowledge of these interactions focusing on the late steps of the virus replication cycle. It builds on our understanding of the cell biology of lipid droplets and the biosynthesis of liver lipoproteins and attempts to explain how HCV hijacks these organelles and pathways to assemble its lipo-viro-particles. In particular, this review describes (i) the mechanisms of viral protein translocation to and from the lipid droplet surface and the orchestration of an interface between replication and assembly complexes, (ii) the importance of the triglyceride mobilization from the lipid droplets for HCV assembly, (iii) the interplay between HCV and the lipoprotein synthesis pathway including the role played by apolipoproteins in virion assembly, and finally (iv) the consequences of these complex virus–host interactions on the virion composition and its biophysical properties. The wealth of data accumulated in the past years on the role of the lipid metabolism in HCV assembly and its imprint on the virion properties will guide vaccine design efforts and reinforce our understanding of the hepatic lipid metabolism in health and disease.

Differential dynamics of hepatic protein expressions with long-term cultivated hepatitis C virus infection

BACKGROUND

The liver maintains blood chemical homeostasis by active uptake and secretion through endocytosis, exocytosis, and intracellular trafficking between the plasma and intracellular membranes. Hepatitis C virus (HCV) infection affects the host membrane architecture and might thus impair the regulation of the cellular transportation machinery. Additionally, the hepatic expressions of differential protein dynamics with long-term HCV infection remain fully recover.

METHODS

In this study, comparative proteomic analysis was performed in HCV-infected and mock-control Huh7 cells according to the viral dynamics of exponential, plateau, declined, and silencing phases at the acute stage, and the chronic stage. The proteins with <0.8-fold and ≥1.25-fold changes in expression were analyzed using functional pathway clustering prediction.

RESULTS

The combined experimental repetitions identified full-spectrum cellular proteins in each of 5 sample sets from acute exponential, plateau, declined, and silencing phases, and the chronic stage. The clustering results revealed that HCV infection might differentiate regulatory pathways involving extracellular exosome, cadherin, melanosome, and RNA binding. Overall host proteins in HCV-infected cells exhibited kinetic pattern 1, in which cellular expression was downregulated from the acute exponential to plateau phases, reached a nadir, and was then elevated at the chronic stage. The proteins involved in the membrane-budding pathway exhibited kinetic pattern 2, in which their expressions were distinctly downregulated at the chronic stage.

CONCLUSION

The current comparative proteomics revealed the differential regulatory effects of HCV infection on host intracellular transport functional pathways, which might contribute to the pathogenic mechanisms of HCV in hepatocytes that sustain long-term infection.

Perilipin-2 is critical for efficient lipoprotein and hepatitis C virus particle production

In hepatocytes, PLIN2 is the major protein coating lipid droplets (LDs), an organelle the hepatitis C virus (HCV) hijacks for virion morphogenesis. We investigated the consequences of PLIN2 deficiency on LDs and on HCV infection. Knockdown of PLIN2 did not affect LD homeostasis, likely due to compensation by PLIN3, but severely impaired HCV particle production. PLIN2-knockdown cells had slightly larger LDs with altered protein composition, enhanced local lipase activity and higher β-oxidation capacity. Electron micrographs showed that, after PLIN2 knockdown, LDs and HCV-induced vesicular structures were tightly surrounded by ER-derived double-membrane sacs. Strikingly, the LD access for HCV core and NS5A proteins was restricted in PLIN2-deficient cells, which correlated with reduced formation of intracellular HCV particles that were less infectious and of higher density, indicating defects in maturation. PLIN2 depletion also reduced protein levels and secretion of ApoE due to lysosomal degradation, but did not affect the density of ApoE-containing lipoproteins. However, ApoE overexpression in PLIN2-deficient cells did not restore HCV spreading. Thus, PLIN2 expression is required for trafficking of core and NS5A proteins to LDs, and for formation of functional low-density HCV particles prior to ApoE incorporation.This article has an associated First Person interview with the first author of the paper.

Functional Characterization of Apolipoproteins in the HCV Life Cycle

Apolipoprotein E (apoE) plays dual functions in the HCV life cycle by promoting HCV infection and virion assembly and production. ApoE is a structural component on the HCV envelope. It mediates HCV cell attachment through specific interactions with the cell surface receptors such as syndecan-1 (SDC-1) and SDC-2 heparan sulfate proteoglycans (HSPGs). It also interacts with NS5A and E2, resulting in an enhancement of HCV morphogenesis. It can bind HCV extracellularly and promotes HCV infection. It is critical for HCV cell-to-cell transmission and may also play a role in HCV persistence by interfering with the action of HCV-neutralizing antibodies. Other apolipoproteins particularly apoB and apoC1 were also found on the HCV envelope, but their roles in the HCV life cycle remain unclear. In the last decade, a number of genomic, immunological, structural, and cell biology methodologies have been developed and used for determining the importance of apoE in the HCV life cycle. These methods and protocols will continue to be valuable to further understand the importance and the underlying molecular mechanism of various apolipoproteins in HCV infection and pathogenesis.

Hypervariable Region 1 in Envelope Protein 2 of Hepatitis C Virus: A Linchpin in Neutralizing Antibody Evasion and Viral Entry

Chronic hepatitis C virus (HCV) infection is the cause of about 400,000 annual liver disease-related deaths. The global spread of this important human pathogen can potentially be prevented through the development of a vaccine, but this challenge has proven difficult, and much remains unknown about the multitude of mechanisms by which this heterogeneous RNA virus evades inactivation by neutralizing antibodies (NAbs). The N-terminal motif of envelope protein 2 (E2), termed hypervariable region 1 (HVR1), changes rapidly in immunoglobulin-competent patients due to antibody-driven antigenic drift. HVR1 contains NAb epitopes and is directly involved in protecting diverse antibody-specific epitopes on E1, E2, and E1/E2 through incompletely understood mechanisms. The ability of HVR1 to protect HCV from NAbs appears linked with modulation of HCV entry co-receptor interactions. Thus, removal of HVR1 increases interaction with CD81, while altering interaction with scavenger receptor class B, type I (SR-BI) in a complex fashion, and decreasing interaction with low-density lipoprotein receptor. Despite intensive efforts this modulation of receptor interactions by HVR1 remains incompletely understood. SR-BI has received the most attention and it appears that HVR1 is involved in a multimodal HCV/SR-BI interaction involving high-density-lipoprotein associated ApoCI, which may prime the virus for later entry events by exposing conserved NAb epitopes, like those in the CD81 binding site. To fully elucidate the multifunctional role of HVR1 in HCV entry and NAb evasion, improved E1/E2 models and comparative studies with other NAb evasion strategies are needed. Derived knowledge may be instrumental in the development of a prophylactic HCV vaccine.

Hepatitis C Virus Envelope Glycoproteins: A Balancing Act of Order and Disorder

Chronic hepatitis C virus infection often leads to liver cirrhosis and primary liver cancer. In 2015, an estimated 71 million people were living with chronic HCV. Although infection rates have decreased in many parts of the world over the last several decades, incidence of HCV infection doubled between 2010 and 2014 in the United States mainly due to increases in intravenous drug use. The approval of direct acting antiviral treatments is a necessary component in the elimination of HCV, but inherent barriers to treatment (e.g., cost, lack of access to healthcare, adherence to treatment, resistance, etc.) prevent dramatic improvements in infection rates. An effective HCV vaccine would significantly slow the spread of the disease. Difficulties in the development of an HCV culture model system and expression of properly folded- and natively modified-HCV envelope glycoproteins E1 and E2 have hindered vaccine development efforts. The recent structural and biophysical studies of these proteins have demonstrated that the binding sites for the cellular receptor CD-81 and neutralizing antibodies are highly flexible in nature, which complicate vaccine design. Furthermore, the interactions between E1 and E2 throughout HCV infection is poorly understood, and structural flexibility may play a role in shielding antigenic epitopes during infection. Here we discuss the structural complexities of HCV E1 and E2.

Hepatitis C Virus (HCV)-Apolipoprotein Interactions and Immune Evasion and Their Impact on HCV Vaccine Design

With more than 71 million people chronically infected, hepatitis C virus (HCV) is one of the leading causes of liver disease and hepatocellular carcinoma. While efficient antiviral therapies have entered clinical standard of care, the development of a protective vaccine is still elusive. Recent studies have shown that the HCV life cycle is closely linked to lipid metabolism. HCV virions associate with hepatocyte-derived lipoproteins to form infectious hybrid particles that have been termed lipo-viro-particles. The close association with lipoproteins is not only critical for virus entry and assembly but also plays an important role during viral pathogenesis and for viral evasion from neutralizing antibodies. In this review, we summarize recent findings on the functional role of apolipoproteins for HCV entry and assembly. Furthermore, we highlight the impact of HCV-apolipoprotein interactions for evasion from neutralizing antibodies and discuss the consequences for antiviral therapy and vaccine design. Understanding these interactions offers novel strategies for the development of an urgently needed protective vaccine.

CD81 Receptor Regions outside the Large Extracellular Loop Determine Hepatitis C Virus Entry into Hepatoma Cells

Hepatitis C virus (HCV) enters human hepatocytes using four essential entry factors, one of which is human CD81 (hCD81). The tetraspanin hCD81 contains a large extracellular loop (LEL), which interacts with the E2 glycoprotein of HCV. The role of the non-LEL regions of hCD81 (intracellular tails, four transmembrane domains, small extracellular loop and intracellular loop) is poorly understood. Here, we studied the contribution of these domains to HCV susceptibility of hepatoma cells by generating chimeras of related tetraspanins with the hCD81 LEL. Our results show that non-LEL regions in addition to the LEL determine susceptibility of cells to HCV. While closely related tetraspanins (X. tropicalis CD81 and D. rerio CD81) functionally complement hCD81 non-LEL regions, distantly related tetraspanins (C. elegans TSP9 amd D. melanogaster TSP96F) do not and tetraspanins with intermediate homology (hCD9) show an intermediate phenotype. Tetraspanin homology and susceptibility to HCV correlate positively. For some chimeras, infectivity correlates with surface expression. In contrast, the hCD9 chimera is fully surface expressed, binds HCV E2 glycoprotein but is impaired in HCV receptor function. We demonstrate that a cholesterol-coordinating glutamate residue in CD81, which hCD9 lacks, promotes HCV infection. This work highlights the hCD81 non-LEL regions as additional HCV susceptibility-determining factors.

Disruption of Claudin-1 Expression by miRNA-182 Alters the Susceptibility to Viral Infectivity in HCV Cell Models

HCV entry involves a complex interplay between viral and host molecules. During post-binding interactions, the viral E2 complexes with CD81 receptor for delivery to the tight junction proteins CLDN1 and OCLN, which aid in viral internalization. Targeting HCV entry receptors represents an appealing approach to inhibit viral infectivity. This study aimed at investigating the impact of targeting CLDN1 by microRNAs on HCV infectivity. miR-155 was previously shown to target the 3′UTR of CLDN1 mRNA. Therefore, miR-155 was used as a control in this study. In-silico analysis and luciferase reporter assay were utilized to identify potential targeting miRNAs. The impact of the identified miRNAs on CLDN1 mRNA and protein expression was examined by qRT-PCR, indirect immunofluorescence and western blotting, respectively. The role of the selected miRNAs on HCV infectivity was assessed by measuring the viral load following the ectopic expression of the selected miRNAs. miR-182 was identified in-silico and by experimental validation to target CLDN1. Both miR-155 and miR-182 inhibited CLDN1 mRNA and protein expression in infected Huh7 cells. Ectopic expression of miR-155 increased, while miR-182 reduced the viral load. In conclusion, despite repressing CLDN1, the impact of miR-155 and miR-182 on HCV infectivity is contradictory. Ectopic miR-182 expression is suggested as an upstream regulator of the entry factor CLDN1, harnessing HCV infection.

Functional innate immunity restricts Hepatitis C Virus infection in induced pluripotent stem cell-derived hepatocytes

Knowledge of activation and interplay between the hepatitis C virus (HCV) and the hosts’ innate immunity is essential to understanding the establishment of chronic HCV infection. Human hepatoma cell lines, widely used as HCV cell culture system, display numerous metabolic alterations and a defective innate immunity, hindering the detailed study of virus-host interactions. Here, we analysed the suitability of induced pluripotent stem cell (iPSC)-derived hepatocyte-like cells (iHLCs) as a physiologically relevant model to study HCV replication in vitro. Density gradients and triglyceride analysis revealed that iHLCs secreted very-low density lipoprotein (VLDL)-like lipoproteins, providing a putative platform for bona fide lipoviroparticles. iHLCs supported the full HCV life cycle, but in contrast to Huh7 and Huh7.5 cells, replication and viral RNA levels decreased continuously. Following HCV infection, interferon-stimulated gene (ISG)-expression significantly increased in iHLCs, whereas induction was almost absent in Huh7/7.5 cells. However, IFNα-stimulation equally induced ISGs in iHLCs and hepatoma cells. JAK-STAT pathway inhibition increased HCV replication in mature iHLCs, but not in Huh7 cells. Additionally, HCV replication levels where higher in STAT2-, but not STAT1-knockdown iHLCs. Our findings support iHLCs as a suitable model for HCV-host interaction regarding a functional innate immunity and lipoprotein synthesis.

Authentic Patient-Derived Hepatitis C Virus Infects and Productively Replicates in Primary CD4+ and CD8+ T Lymphocytes In Vitro

Accumulated evidence indicates that immune cells can support the replication of hepatitis C virus (HCV) in infected patients and in culture. However, there is a scarcity of data on the degree to which individual immune cell types support HCV propagation and on characteristics of virus assembly. We investigated the ability of authentic, patient-derived HCV to infect in vitro two closely related but functionally distinct immune cell types, CD4⁺ and CD8⁺ T lymphocytes, and assessed the properties of the virus produced by these cells. The HCV replication system in intermittently mitogen-stimulated T cells was adapted to infect primary human CD4⁺ or CD8⁺ T lymphocytes. HCV replicated in both cell types although at significantly higher levels in CD4⁺ than in CD8⁺ T cells. Thus, the HCV RNA replicative (negative) strand was detected in CD4⁺ and CD8⁺ cells at estimated mean levels ± standard errors of the means of 6.7 × 10² ± 3.8 × 10² and 1.2 × 10² ± 0.8 × 10² copies/μg RNA, respectively (P < 0.0001). Intracellular HCV NS5a and/or core proteins were identified in 0.9% of CD4⁺ and in 1.2% of CD8⁺ T cells. Double staining for NS5a and T cell type-specific markers confirmed that transcriptionally competent virus replicated in both cell types. Furthermore, an HCV-specific protease inhibitor, telaprevir, inhibited infection in both CD4⁺ and CD8⁺ cells. The emergence of unique HCV variants and the release of HCV RNA-reactive particles with biophysical properties different from those of virions in plasma inocula suggested that distinct viral particles were assembled, and therefore, they may contribute to the pool of circulating virus in infected patients.IMPORTANCE Although the liver is the main site of HCV replication, infection of the immune system is an intrinsic characteristic of this virus independent of whether infection is symptomatic or clinically silent. Many fundamental aspects of HCV lymphotropism remain uncertain, including the degree to which different immune cells support infection and contribute to virus diversity. We show that authentic, patient-derived HCV productively replicates in vitro in two closely related but functionally distinct types of T lymphocytes, CD4⁺ and CD8⁺ cells. The display of viral proteins and unique variants, the production of virions with biophysical properties distinct from those in plasma serving as inocula, and inhibition of replication by an antiviral agent led us to ascertain that both T cell subtypes supported virus propagation. Infection of CD4⁺ and CD8⁺ T cells, which are central to adaptive antiviral immune responses, can directly affect HCV clearance, favor virus persistence, and decisively influence the development and progression of hepatitis C.

Lysophosphatidylcholine acyltransferase 1 is downregulated by hepatitis C virus: impact on production of lipo-viro-particles

OBJECTIVE

HCV is intimately linked with the liver lipid metabolism, devoted to the efflux of triacylglycerols stored in lipid droplets (LDs) in the form of triacylglycerol-rich very-low-density lipoproteins (VLDLs): (i) the most infectious HCV particles are those of lowest density due to association with triacylglycerol-rich lipoproteins and (ii) HCV-infected patients frequently develop hepatic steatosis (increased triacylglycerol storage). The recent identification of lysophosphatidylcholine acyltransferase 1 (LPCAT1) as an LD phospholipid-remodelling enzyme prompted us to investigate its role in liver lipid metabolism and HCV infectious cycle.

DESIGN

Huh-7.5.1 cells and primary human hepatocytes (PHHs) were infected with JFH1-HCV. LPCAT1 depletion was achieved by RNA interference. Cells were monitored for LPCAT1 expression, lipid metabolism and HCV production and infectivity. The density of viral particles was assessed by isopycnic ultracentrifugation.

RESULTS

Upon HCV infection, both Huh-7.5.1 cells and PHH had decreased levels of LPCAT1 transcript and protein, consistent with transcriptional downregulation. LPCAT1 depletion in either naive or infected Huh-7.5.1 cells resulted in altered lipid metabolism characterised by LD remodelling, increased triacylglycerol storage and increased secretion of VLDL. In infected Huh-7.5.1 cells or PHH, LPCAT1 depletion increased production of the viral particles of lowest density and highest infectivity.

CONCLUSIONS

We have identified LPCAT1 as a modulator of liver lipid metabolism downregulated by HCV, which appears as a viral strategy to increase the triacylglycerol content and hence infectivity of viral particles. Targeting this metabolic pathway may represent an attractive therapeutic approach to reduce both the viral titre and hepatic steatosis.

Newly discovered hepatitis C virus minicores circulate in human blood

Hepatitis C virus (HCV) is one of the most prevalent causes of chronic blood‐borne infections worldwide. Despite developments of highly effective treatments, most infected individuals are unaware of their infection. Approximately 75% of infections are in low‐ and middle‐income countries; therefore, continuing research in HCV molecular virology and the development of vaccines and affordable diagnostics is required to reduce the global burden. Various intracellular forms of the HCV nucleocapsid (core) protein are produced in cell culture; these comprise the conventional p21 core and the newly discovered shorter isoforms (minicores). Minicores lack the N‐terminus of p21 core. This study was conducted to determine if minicores are secreted in cell culture and more importantly if they circulate in the blood of individuals infected with HCV. We also developed a new monoclonal antibody that detects minicores targeting a C‐terminal region common to p21 core and minicores. Direct evidence of minicores requires western blot analysis to distinguish the detection of p21 core from minicores. However, the sensitivity for western blot detection of HCV proteins from blood is nil without their prior purification/enrichment from blood. Therefore, we developed a purification method based on a heparin/Mn⁺² precipitation of apolipoprotein B‐containing lipoproteins because HCV is thought to circulate as a hybrid lipoviral particle. Minicores are secreted in culture when cells are grown in the presence of human serum. The heparin/Mn⁺² precipitate from HCV‐infected cell culture supernatants and from the blood of 4 patients with high‐titer genotype‐1 HCV contained minicores. Conclusion: Minicores are major newly discovered HCV proteins that are secreted and circulate in blood during natural infections. Minicore proteins have translational potential as targets in diagnostic assays and in vaccine development. (Hepatology Communications 2018;2:21–28)

Avasimibe: A novel hepatitis C virus inhibitor that targets the assembly of infectious viral particles

Direct-acting antivirals (DAAs), which target hepatitis C virus (HCV) proteins, have exhibited impressive efficacy in the management of chronic hepatitis C. However, the concerns regarding high costs, drug resistance mutations and subsequent unexpected side effects still call for the development of host-targeting agents (HTAs) that target host factors involved in the viral life cycle and exhibit pan-genotypic antiviral activity. Given the close relationship between lipid metabolism and the HCV life cycle, we investigated the anti-HCV activity of a series of lipid-lowering drugs that have been approved by government administrations or proven safety in clinical trials. Our results showed that avasimibe, an inhibitor of acyl coenzyme A:cholesterol acyltransferase (ACAT), exhibited marked pan-genotypic inhibitory activity and superior inhibition against HCV when combined with DAAs. Moreover, avasimibe significantly impaired the assembly of infectious HCV virions. Mechanistic studies demonstrated that avasimibe induced downregulation of microsomal triglyceride transfer protein expression, resulting in reduced apolipoprotein E and apolipoprotein B secretion. Therefore, the pan-genotypic antiviral activity and clinically proven safety endow avasimibe exceptional potential as a candidate for combination therapy with DAAs. In addition, the discovery of the antiviral properties of ACAT inhibitors also suggests that inhibiting the synthesis of cholesteryl esters might be an additional target for the therapeutic intervention for chronic HCV infection.

Impact of Apo E gene polymorphism on HCV therapy related outcome in a cohort of HCV Egyptian patients

The functional apolipoprotein E (Apo E) gene polymorphism could be used as a determinant of outcome of HCV infection. This study aimed to demonstrate the impact of Apo E genotype on the response to HCV combined therapy.

MATERIAL AND METHODS

The study has been implemented on 125 individuals with persistent HCV infection and 120 cases with sustained virologic response (SVR). All participants were genotyped for ApoE gene polymorphism by a real-time quantitative PCR (qPCR).

RESULTS

Statistically significant differences were demonstrated regarding the Apo E genotypes between the two groups (P-value < .001) where the frequency of E3E3 was significantly higher among the chronic HCV-patients while E3E4 and E4E4 genotypes frequencies were higher among the SVR-subjects group and E3E3 genotype was associated with increased risk of chronicity (OR 4.7; 95% CI 1.9-12.1, P-value < .001). Moreover, There were statically significant differences regarding E3 and E4 alleles frequencies, where E3 allele display a higher frequency among the chronic HCV-patient group while the SVR-subjects group showed higher frequency of E4 allele and the carriers of E3 allele have 1.4 times more risk to develop chronicity than those with E4 allele (OR 1.4; 95% CI 1.0-2.0, P-value < .05). Meanwhile the protective E2 allele was absent in all infected participants.

CONCLUSION

This study supports the hypothesis of the protective impact of Apo E4 allele that favors viral clearance of HCV infection and its recovery after combined therapy, while the Apo E3 allele is considered as a particular risk factor for the chronicity in HCV patients and resistance to therapy. Whereas the Apo E2 allele confers a resistance to HCV infection at a time of exposure.

Pentagalloylglucose, a highly bioavailable polyphenolic compound present in Cortex moutan, efficiently blocks hepatitis C virus entry

Approximately 142 million people worldwide are infected with hepatitis C virus (HCV). Although potent direct acting antivirals are available, high costs limit access to treatment. Chronic hepatitis C virus infection remains a major cause of orthotopic liver transplantation. Moreover, re-infection of the graft occurs regularly. Antivirals derived from natural sources might be an alternative and cost-effective option to complement therapy regimens for global control of hepatitis C virus infection. We tested the antiviral properties of a mixture of different Chinese herbs/roots named Zhi Bai Di Huang Wan (ZBDHW) and its individual components on HCV. One of the ZBDHW components, Penta-O-Galloyl-Glucose (PGG), was further analyzed for its mode of action in vitro, its antiviral activity in primary human hepatocytes as well as for its bioavailability and hepatotoxicity in mice. ZBDHW, its component Cortex Moutan and the compound PGG efficiently block entry of HCV of all major genotypes and also of the related flavivirus Zika virus. PGG does not disrupt HCV virion integrity and acts primarily during virus attachment. PGG shows an additive effect when combined with the well characterized HCV inhibitor Daclatasvir. Analysis of bioavailability in mice revealed plasma levels above tissue culture IC₅₀ after a single intraperitoneal injection. In conclusion, PGG is a pangenotypic HCV entry inhibitor with high bioavailability. The low cost and wide availability of this compound make it a promising candidate for HCV combination therapies, and also emerging human pathogenic flaviviruses like ZIKV.

Hepatitis C Virus Strain-Dependent Usage of Apolipoprotein E Modulates Assembly Efficiency and Specific Infectivity of Secreted Virions

Hepatitis C virus (HCV) is extraordinarily diverse and uses entry factors in a strain-specific manner. Virus particles associate with lipoproteins, and apolipoprotein E (ApoE) is critical for HCV assembly and infectivity. However, whether ApoE dependency is common to all HCV genotypes remains unknown. Therefore, we compared the roles of ApoE utilizing 10 virus strains from genotypes 1 through 7. ApoA and ApoC also support HCV assembly, so they may contribute to virus production in a strain-dependent fashion. Transcriptome sequencing (RNA-seq) revealed abundant coexpression of ApoE, ApoB, ApoA1, ApoA2, ApoC1, ApoC2, and ApoC3 in primary hepatocytes and in Huh-7.5 cells. Virus production was examined in Huh-7.5 cells with and without ApoE expression and in 293T cells where individual apolipoproteins (ApoE1, -E2, -E3, -A1, -A2, -C1, and -C3) were provided in trans All strains were strictly ApoE dependent. However, ApoE involvement in virus production was strain and cell type specific, because some HCV strains poorly produced infectious virus in ApoE-expressing 293T cells and because ApoE knockout differentially affected virus production of HCV strains in Huh-7.5 cells. ApoE allelic isoforms (ApoE2, -E3, and -E4) complemented virus production of HCV strains to comparable degrees. All tested strains assembled infectious progeny with ApoE in preference to other exchangeable apolipoproteins (ApoA1, -A2, -C1, and -C3). The specific infectivity of HCV particles was similar for 293T- and Huh-7.5-derived particles for most strains; however, it differed by more than 100-fold in some viruses. Collectively, this study reveals strain-dependent and host cell-dependent use of ApoE during HCV assembly. These differences relate to the efficacy of virus production and also to the properties of released virus particles and therefore govern viral fitness at the level of assembly and cell entry.IMPORTANCE Chronic HCV infections are a major cause of liver disease. HCV is highly variable, and strain-specific determinants modulate the response to antiviral therapy, the natural course of infection, and cell entry factor usage. Here we explored whether host factor dependency of HCV in particle assembly is modulated by strain-dependent viral properties. We showed that all examined HCV strains, which represent all seven known genotypes, rely on ApoE expression for assembly of infectious progeny. However, the degree of ApoE dependence is modulated in a strain-specific and cell type-dependent manner. This indicates that HCV strains differ in their assembly properties and host factor usage during assembly of infectious progeny. Importantly, these differences relate not only to the efficiency of virus production and release but also to the infectiousness of virus particles. Thus, strain-dependent features of HCV modulate ApoE usage, with implications for virus fitness at the level of assembly and cell entry.

Permissiveness of human hepatocellular carcinoma cell lines for hepatitis C virus entry and replication

Hepatitis C virus (HCV) is a globally prevalent pathogen and is associated with high death rates and morbidity. Since its discovery in 1989, HCV research has been impeded by the lack of a robust infectious cell culture system and thus in vitro studies on diverse genetic backgrounds are hampered because of the limited number of hepatoma cell lines which are able to support different aspects of the HCV life cycle. In the current study, we sought to expand the limited number of permissive cells capable of supporting the diverse phases of the HCV life cycle. Initially, we screened a panel of new hepatoma-derived cell lines, designated BCLC-1, -2, -3, -4, -5, -6, -9 and -10 cells, for their ability to express essential HCV receptors and subsequently to support HCV entry by using the well-characterized HCV pseudoparticle system (HCVpp). Apart from BCLC-9, all BCLC cell lines were permissive for HCVpp infection. Next, BCLC cells were subjected to short- and long-term HCV RNA replication studies using HCV subgenomic replicons. Interestingly, only BCLC-1, -5 and -9 cells, supported short-term HCV RNA replication, but the latter were excluded from further studies since they were refractory for HCV entry. BCLC-1, -5 were able to support long-term HCV replication too; yet BCLC-5 cells supported the highest long-term HCV RNA replication levels. Furthermore, cured BCLC-5 clones from HCV subgenomic replicon, showed increased permissiveness for HCV RNA replication. Strikingly, we were unable to detect endogenous BCLC-5 miR122 expression - an important HCV host factor- and as expected, the exogenous expression of miR122 in BCLC-5 cells increased their permissiveness for HCV RNA replication. However, this cell line was unable to produce HCV infectious particles despite ectopic expression of apolipoprotein E, which in other hepatoma cell lines has been shown to be sufficient to enable the HCV secretion process, suggesting a lack of other host cellular factor(s) and/or the presence of inhibitory factor(s). In conclusion, the establishment of these new permissive cell lines for HCV entry and replication, which possess a different genetic background compared to the well-established models, expands the current repertoire of hepatoma cell lines susceptible to the study of the HCV life cycle and also will aid to further elucidate the cellular determinants that modulate HCV replication, assembly and egress.

Hepatitis C Virus Lipoviroparticles Assemble in the Endoplasmic Reticulum (ER) and Bud off from the ER to the Golgi Compartment in COPII Vesicles

Hepatitis C virus (HCV) exists as a lipoprotein-virus hybrid lipoviroparticle (LVP). In vitro studies have demonstrated the importance of apolipoproteins in HCV secretion and infectivity, leading to the notion that HCV coopts the secretion of very-low-density lipoprotein (VLDL) for its egress. However, the mechanisms involved in virus particle assembly and egress are still elusive. The biogenesis of VLDL particles occurs in the endoplasmic reticulum (ER), followed by subsequent lipidation in the ER and Golgi compartment. The secretion of mature VLDL particles occurs through the Golgi secretory pathway. HCV virions are believed to latch onto or fuse with the nascent VLDL particle in either the ER or the Golgi compartment, resulting in the generation of LVPs. In our attempt to unravel the collaboration between HCV and VLDL secretion, we studied HCV particles budding from the ER en route to the Golgi compartment in COPII vesicles. Biophysical characterization of COPII vesicles fractionated on an iodixanol gradient revealed that HCV RNA is enriched in the highly buoyant COPII vesicle fractions and cofractionates with apolipoprotein B (ApoB), ApoE, and the HCV core and envelope proteins. Electron microscopy of immunogold-labeled microsections revealed that the HCV envelope and core proteins colocalize with apolipoproteins and HCV RNA in Sec31-coated COPII vesicles. Ultrastructural analysis also revealed the presence of HCV structural proteins, RNA, and apolipoproteins in the Golgi stacks. These findings support the hypothesis that HCV LVPs assemble in the ER and are transported to the Golgi compartment in COPII vesicles to embark on the Golgi secretory route.IMPORTANCE HCV assembly and release accompany the formation of LVPs that circulate in the sera of HCV patients and are also produced in an in vitro culture system. The pathway of HCV morphogenesis and secretion has not been fully understood. This study investigates the exact site where the association of HCV virions with host lipoproteins occurs. Using immunoprecipitation of COPII vesicles and immunogold electron microscopy (EM), we characterize the existence of LVPs that cofractionate with lipoproteins, viral proteins, RNA, and vesicular components. Our results show that this assembly occurs in the ER, and LVPs thus formed are carried through the Golgi network by vesicular transport. This work provides a unique insight into the HCV LVP assembly process within infected cells and offers opportunities for designing antiviral therapeutic cellular targets.

Hepatitis C virus-apolipoprotein interactions: molecular mechanisms and clinical impact

INTRODUCTION

Chronic hepatitis C virus (HCV) infection is a leading cause of cirrhosis, hepatocellular carcinoma and liver failure. Moreover, chronic HCV infection is associated with liver steatosis and metabolic disorders. With 130-150 million people chronically infected in the world, HCV infection represents a major public health problem. One hallmark on the virus is its close link with hepatic lipid and lipoprotein metabolism. Areas covered: HCV is associated with lipoprotein components such as apolipoproteins. These interactions play a key role in the viral life cycle, viral persistence and pathogenesis of liver disease. This review introduces first the role of apolipoproteins in lipoprotein metabolism, then highlights the molecular mechanisms of HCV-lipoprotein interactions and finally discusses their clinical impact. Expert commentary: While the study of virus-host interactions has resulted in a improvement of the understanding of the viral life cycle and the development of highly efficient therapies, major challenges remain: access to therapy is limited and an urgently needed HCV vaccine remains still elusive. Furthermore, the pathogenesis of disease biology is still only partially understood. The investigation of HCV-lipoproteins interactions offers new perspectives for novel therapeutic approaches, contribute to HCV vaccine design and understand virus-induced liver disease and cancer.

The Plasma and Serum Metabotyping of Hepatocellular Carcinoma in a Nigerian and Egyptian Cohort using Proton Nuclear Magnetic Resonance Spectroscopy

BACKGROUND/AIMS

Previous studies have observed disturbances in the ¹H nuclear magnetic resonance (NMR) blood spectral profiles in malignancy. No study has metabotyped serum or plasma of hepatocellular carcinoma (HCC) patients from two diverse populations. We aimed to delineate the HCC patient metabotype from Nigeria (mostly hepatitis B virus infected) and Egypt (mostly hepatitis C virus infected) to explore lipid and energy metabolite alterations that may be independent of disease aetiology, diet and environment.

METHODS

Patients with HCC (53) and cirrhosis (26) and healthy volunteers (19) were recruited from Nigeria and Egypt. Participants provided serum or plasma samples, which were analysed using 600 MHz ¹H NMR spectroscopy with nuclear Overhauser enhancement spectroscopy pulse sequences. Median group spectra comparison and multivariate analysis were performed to identify regions of difference.

RESULTS

Significant differences between HCC patients and healthy volunteers were detected in levels of low density lipoprotein (P = 0.002), very low density lipoprotein (P < 0.001) and lactate (P = 0.03). N-acetylglycoproteins levels in HCC patients were significantly different from both healthy controls and cirrhosis patients (P < 0.001 and 0.001).

CONCLUSION

Metabotype differences were present, pointing to disturbed lipid metabolism and a switch from glycolysis to alternative energy metabolites with malignancy, which supports the Warburg hypothesis of tumour metabolism.

Live cell imaging and analysis of lipid droplets biogenesis in hepatatis C virus infected cells

Lipid droplets (LDs) are regulated neutral lipid storage organelles having a central role in numerous cellular processes as well as in various pathologies such as metabolic disorders, immune responses and during pathogen infection. Due to the growing significance of LDs, extensive efforts are made to study the mechanism and the dynamics of their formation and life history and how are these diverted or modified by pathogens. Real-time visualization of lipid droplet biogenesis can assist in clarifying these and other important issues and may have implications towards understanding the pathogenesis of the associated diseases. Typically, LDs are post-experimentally stained using lipophilic dyes and are visualized under a microscope. Alternatively, overexpression of LD-associated proteins or immunofluorescence analyses are used to identify and follow LDs. These experimental approaches only examine a single end point of the experiment and cannot answer questions regarding LD dynamics. Here, we describe a simple and novel experimental setting that allows real-time fluorescence staining and detection of LDs in cultured living as well as infected cells. This method is quick and simple and is not restricted to a specific dye or cell line. Using this system, the biogenesis of LDs and their growth is demonstrated in cells infected with hepatitis C virus (HCV), confirming the strength of this method and the wide range of its applications.

Regulated Entry of Hepatitis C Virus into Hepatocytes

Hepatitis C virus (HCV) is a model for the study of virus–host interaction and host cell responses to infection. Virus entry into hepatocytes is the first step in the HCV life cycle, and this process requires multiple receptors working together. The scavenger receptor class B type I (SR-BI) and claudin-1 (CLDN1), together with human cluster of differentiation (CD) 81 and occludin (OCLN), constitute the minimal set of HCV entry receptors. Nevertheless, HCV entry is a complex process involving multiple host signaling pathways that form a systematic regulatory network; this network is centrally controlled by upstream regulators epidermal growth factor receptor (EGFR) and transforming growth factor β receptor (TGFβ-R). Further feedback regulation and cell-to-cell spread of the virus contribute to the chronic maintenance of HCV infection. A comprehensive and accurate disclosure of this critical process should provide insights into the viral entry mechanism, and offer new strategies for treatment regimens and targets for HCV therapeutics.

Role of cleavage at the core-E1 junction of hepatitis C virus polyprotein in viral morphogenesis

In hepatitis C virus (HCV) polyprotein sequence, core protein terminates with E1 envelope signal peptide. Cleavage by signal peptidase (SP) separates E1 from the complete form of core protein, anchored in the endoplasmic reticulum (ER) membrane by the signal peptide. Subsequent cleavage of the signal peptide by signal-peptide peptidase (SPP) releases the mature form of core protein, which preferentially relocates to lipid droplets. Both of these cleavages are required for the HCV infectious cycle, supporting the idea that HCV assembly begins at the surface of lipid droplets, yet SPP-catalyzed cleavage is dispensable for initiation of budding in the ER. Here we have addressed at what step(s) of the HCV infectious cycle SP-catalyzed cleavage at the core-E1 junction is required. Taking advantage of the sole system that has allowed visualization of HCV budding events in the ER lumen of mammalian cells, we showed that, unexpectedly, mutations abolishing this cleavage did not prevent but instead tended to promote the initiation of viral budding. Moreover, even though no viral particles were released from Huh-7 cells transfected with a full-length HCV genome bearing these mutations, intracellular viral particles containing core protein protected by a membrane envelope were formed. These were visualized by electron microscopy as capsid-containing particles with a diameter of about 70 nm and 40 nm before and after delipidation, respectively, comparable to intracellular wild-type particle precursors except that they were non-infectious. Thus, our results show that SP-catalyzed cleavage is dispensable for HCV budding per se, but is required for the viral particles to acquire their infectivity and secretion. These data support the idea that HCV assembly occurs in concert with budding at the ER membrane. Furthermore, capsid-containing particles did not accumulate in the absence of SP-catalyzed cleavage, suggesting the quality of newly formed viral particles is controlled before secretion.

Hepatitis C Virus-Genotype 3: Update on Current and Emergent Therapeutic Interventions

PURPOSE OF REVIEW

Direct-acting antiviral agents (DAAs) have markedly improved the prognosis of hepatitis C virus (HCV)-genotype 3 (GT3), a highly prevalent infection worldwide. However, in patients with hepatic fibrosis, cirrhosis, or hepatocellular carcinoma (HCC), GT3 infection presents a treatment challenge compared with other genotypes. The dependence of the HCV life cycle on host lipid metabolism suggests the possible utility of targeting host cellular factors for combination anti-HCV therapy. We discuss current and emergent DAA regimens for HCV-GT3 treatment. We then summarize recent research findings on the reliance of HCV entry, replication, and virion assembly on host lipid metabolism.

RECENT FINDINGS

Current HCV treatment guidelines recommend the use of daclatasvir plus sofosbuvir (DCV/SOF) or sofosbuvir plus velpatasvir (SOF/VEL) for the management of GT3 based upon clinical efficacy [≥88% overall sustained virological response (SVR)] and tolerability. Potential future DAA options, such as SOF/VEL co-formulated with GS-9857, also look promising in treating cirrhotic GT3 patients. However, HCV resistance to DAAs will likely continue to impact the therapeutic efficacy of interferon-free treatment regimens. Disruption of HCV entry by targeting required host cellular receptors shows potential in minimizing HCV resistance and broadening therapeutic options for certain subpopulations of GT3 patients. The use of cholesterol biosynthesis and transport inhibitors may also improve health outcomes for GT3 patients when used synergistically with DAAs. Due to the morbidity and mortality associated with HCV-GT3 infection compared to other genotypes, efforts should be made to address current limitations in the therapeutic prevention and management of HCV-GT3 infection.