An overview: in vitro models of HCV replication in different cell cultures

Hepatitis C Virus Entry into Macrophages/Monocytes Mainly Depends on the Phagocytosis of Macrophages

BACKGROUND

Hepatitis C virus (HCV) has been classified as a strictly hepatotropic pathogen for a long time, and hepatocytes are target cells for HCV infection. More and more studies showed non-liver cells supported HCV entry and replication, such as macrophages. The mechanisms of HCV entry into macrophages are still not clear.

AIMS

This study aims to determine the way of HCV entry into macrophages.

METHODS

Cell culture-derived infectious HCV particles (HCVcc) were prepared using Huh7 cells transfected with HCV RNA. CD81-knockdown cells were obtained through siRNA transfection. HCV RNA levels were determined by RT-qPCR. Flow cytometry analyses were used to determine cell surface levels of CD11b, CD68, and CD81. ELISA and western blotting were performed to quantify the protein levels of IL-1β, IL-6, and TNF-α. Phagocytic ability was determined by neutral red uptake assay.

RESULTS

CD81 knockdown could not inhibit HCVcc entry into macrophages. The entry of HCV into macrophages could not be blocked by pooled IgG from chronic hepatitis C patient's sera. Macrophages derived from THP-1 cells displayed stronger phagocytic capacity, which also swallowed more HCV RNA. Treatment of macrophages with endocytic inhibitor, methyl-β-cyclodextrin, decreased the internalization of HCV. HCV uptake by macrophages was related to the reorganization of F-actin cytoskeleton and PI3Ks activation. HCV infection significantly increased the expression of IL1β and IL6 in macrophages and promoted apoptosis of macrophages.

CONCLUSIONS

HCV entry into macrophages mainly depends on phagocytosis of macrophages.

Efficient replication of blood-borne hepatitis C virus in human fetal liver stem cells

The development of pathogenic mechanisms, specific antiviral treatments and preventive vaccines for hepatitis C virus (HCV) infection has been limited due to lack of cell culture models that can naturally imitate the entire HCV life cycle. Here, we established an HCV cell culture model based on human fetal liver stem cells (hFLSCs) that supports the entire blood-borne hepatitis C virus (bbHCV) life cycle. More than 90% of cells remained infected by various genotypes. bbHCV was efficiently propagated, and progeny virus were infectious to hFLSCs. The virus could be passed efficiently between cells. The viral infectivity was partially blocked by specific antibodies or small interfering RNA against HCV entry factors, whereas HCV replication was inhibited by antiviral drugs. We observed viral particles of approximately 55 nm in diameter in both cell culture media and infected cells after bbHCV infection.

CONCLUSION

Our data show that the entire bbHCV life cycle could be naturally imitated in hFLSCs. This model is expected to provide a powerful tool for exploring the process and the mechanism of bbHCV infection at the cellular level and for evaluating the treatment and preventive strategies of bbHCV infection. (Hepatology 2017;66:1045-1057).

A robust model of natural hepatitis C infection using hepatocyte-like cells derived from human induced pluripotent stem cells as a long-term host

BACKGROUND

Hepatitis C virus (HCV) could induce chronic liver diseases and hepatocellular carcinoma in human. The use of primary human hepatocyte as a viral host is restrained with the scarcity of tissue supply. A culture model restricted to HCV genotype 2a (JFH-1) has been established using Huh7-derived hepatocyte. Other genotypes including the wild-type virus could not propagate in Huh7, Huh7.5 and Huh7.5.1 cells.

METHODS

Functional hepatocyte-like cells (HLCs) were developed from normal human iPS cells as a host for HCV infection. Mature HLCs were identified for selective hepatocyte markers, CYP450s, HCV associated receptors and HCV essential host factors. HLCs were either transfected with JFH-1 HCV RNA or infected with HCV particles derived from patient serum. The enhancing effect of α-tocopherol and the inhibitory effects of INF-α, ribavirin and sofosbuvir to HCV infection were studied. The HCV viral load and HCV RNA were assayed for the infection efficiency.

RESULTS

The fully-developed HLCs expressed phase I, II, and III drug-metabolizing enzymes, HCV associated receptors (claudin-1, occludin, CD81, ApoE, ApoB, LDL-R) and HCV essential host factors (miR-122 and SEC14L2) comparable to the primary human hepatocyte. SEC14L2, an α-tocopherol transfer protein, was expressed in HLCs, but not in Huh7 cell, had been implicated in effective HCVser infection. The HLCs permitted not only the replication of HCV RNA, but also the production of HCV particles (HCVcc) released to the culture media. HLCs drove higher propagation of HCVcc derived from JFH-1 than did the classical host Huh7 cells. HLCs infected with either JFH-1 or wild-type HCV expressed HCV core antigen, NS5A, NS5B, NS3 and HCV negative-stand RNA. HLCs allowed entire HCV life cycle derived from either JFH-1, HCVcc or wild-type HCV (genotype 1a, 1b, 3a, 3b, 6f and 6n). Further increasing the HCVser infection in HLCs was achieved by incubating cell with α-tocopherol. The supernatant from infected HLCs could infect both naïve HLC and Huh7 cell. Treating infected HLC with INF-α and ribavirin decreased HCV RNA in both the cellular fraction and the culture medium. The HLCs reacted to HCVcc or wild-type HCV infection by upregulating TNF-α, IL-28B and IL-29.

CONCLUSIONS

This robust cell culture model for serum-derived HCV using HLCs as host cells provides a remarkable system for investigating HCV life cycle, HCV-associated hepatocellular carcinoma development and the screening for new anti HCV drugs.

Explanted diseased livers - a possible source of metabolic competent primary human hepatocytes

Being an integral part of basic, translational and clinical research, the demand for primary human hepatocytes (PHH) is continuously growing while the availability of tissue resection material for the isolation of metabolically competent PHH remains limited. To overcome current shortcomings, this study evaluated the use of explanted diseased organs from liver transplantation patients as a potential source of PHH. Therefore, PHH were isolated from resected surgical specimens (Rx-group; n = 60) and explanted diseased livers obtained from graft recipients with low labMELD-score (Ex-group; n = 5). Using established protocols PHH were subsequently cultured for a period of 7 days. The viability and metabolic competence of cultured PHH was assessed by the following parameters: morphology and cell count (CyQuant assay), albumin synthesis, urea production, AST-leakage, and phase I and II metabolism. Both groups were compared in terms of cell yield and metabolic function, and results were correlated with clinical parameters of tissue donors. Notably, cellular yields and viabilities were comparable between the Rx- and Ex-group and were 5.3±0.5 and 2.9±0.7×10⁶ cells/g liver tissue with 84.3±1.3 and 76.0±8.6% viability, respectively. Moreover, PHH isolated from the Rx- or Ex-group did not differ in regards to loss of cell number in culture, albumin synthesis, urea production, AST-leakage, and phase I and II metabolism (measured by the 7-ethoxycoumarin-O-deethylase and uracil-5′-diphosphate-glucuronyltransferase activity). Likewise, basal transcript expressions of the CYP monooxygenases 1A1, 2C8 and 3A4 were comparable as was their induction when treated with a cocktail that consisted of 3-methylcholantren, rifampicin and phenobarbital, with increased expression of CYP 1A1 and 3A4 mRNA while transcript expression of CYP 2C8 was only marginally changed. In conclusion, the use of explanted diseased livers obtained from recipients with low labMELD-score might represent a valuable source of metabolically competent PHH which are comparable in viability and function to cells obtained from specimens following partial liver resection.

Oxysterol-binding protein is a phosphatidylinositol 4-kinase effector required for HCV replication membrane integrity and cholesterol trafficking

BACKGROUND & AIMS

Positive-sense RNA viruses remodel intracellular membranes to generate specialized membrane compartments for viral replication. Several RNA viruses, including poliovirus and hepatitis C virus (HCV), require phosphatidylinositol (PI) 4-kinases for their replication. However, it is not known how PI 4-kinases and their product, PI(4)P, facilitate host membrane reorganization and viral replication. In addition, although the HCV replication compartment, known as the membranous web, is believed to be cholesterol enriched, the mechanisms by which this occurs have not been elucidated. We aimed to identify and characterize a PI 4-kinase effector in HCV replication.

METHODS

We used a combination of microscopic and biochemical methods to study HCV replication, web morphology, the distribution of intracellular protein and PI(4)P, along with cholesterol trafficking in HCV-infected cells. PI 4-kinase and oxysterol-binding protein (OSBP) were inhibited using RNA interference or small molecules in cells expressing a full-length genotype 1b replicon or infected with the JFH-1 strain of HCV.

RESULTS

OSBP was required for HCV replication and membranous web integrity. OSBP was recruited to membranous webs in a PI 4-kinase-dependent manner, and both these factors were found to regulate cholesterol trafficking to the web. We also found OSBP to be required for poliovirus infection but dispensable for dengue virus.

CONCLUSIONS

OSBP is a PI 4-kinase effector in HCV infection, and contributes to the integrity and cholesterol enrichment of the membranous web. OSBP might also be a PI 4-kinase effector in poliovirus infection and could be involved in replication of other viruses that require PI 4-kinases.

Novel permissive cell lines for complete propagation of hepatitis C virus

Hepatitis C virus (HCV) is a major etiologic agent of chronic liver diseases. Although the HCV life cycle has been clarified by studying laboratory strains of HCV derived from the genotype 2a JFH-1 strain (cell culture-adapted HCV [HCVcc]), the mechanisms of particle formation have not been elucidated. Recently, we showed that exogenous expression of a liver-specific microRNA, miR-122, in nonhepatic cell lines facilitates efficient replication but not particle production of HCVcc, suggesting that liver-specific host factors are required for infectious particle formation. In this study, we screened human cancer cell lines for expression of the liver-specific α-fetoprotein by using a cDNA array database and identified liver-derived JHH-4 cells and stomach-derived FU97 cells, which express liver-specific host factors comparable to Huh7 cells. These cell lines permit not only replication of HCV RNA but also particle formation upon infection with HCVcc, suggesting that hepatic differentiation participates in the expression of liver-specific host factors required for HCV propagation. HCV inhibitors targeting host and viral factors exhibited different antiviral efficacies between Huh7 and FU97 cells. Furthermore, FU97 cells exhibited higher susceptibility for propagation of HCVcc derived from the JFH-2 strain than Huh7 cells. These results suggest that hepatic differentiation participates in the expression of liver-specific host factors required for complete propagation of HCV.

IMPORTANCE

Previous studies have shown that liver-specific host factors are required for efficient replication of HCV RNA and formation of infectious particles. In this study, we screened human cancer cell lines for expression of the liver-specific α-fetoprotein by using a cDNA array database and identified novel permissive cell lines for complete propagation of HCVcc without any artificial manipulation. In particular, gastric cancer-derived FU97 cells exhibited a much higher susceptibility to HCVcc/JFH-2 infection than observed in Huh7 cells, suggesting that FU97 cells would be useful for further investigation of the HCV life cycle, as well as the development of therapeutic agents for chronic hepatitis C.

Detection of hepatitis C virus (HCV) negative strand RNA and NS3 protein in peripheral blood mononuclear cells (PBMC): CD3+, CD14+ and CD19+

Background

Although hepatitis C virus (HCV) is primarily hepatotropic, markers of HCV replication were detected in peripheral blood mononuclear cells (PBMC) as well as in ex vivo collected tissues and organs. Specific strains of HCV were found to be capable to infect cells of the immune system: T and B cells and monocytes/macrophages as well as cell lines in vitro. The direct invasion of cells of the immune system by the virus may be responsible for extrahepatic consequences of HCV infection: cryoglobulinemia and non-Hodgkin’s lymphoma.

The aim of the present study was to determine the prevalence of markers of HCV infection: negative strand HCV RNA and non-structural NS3 protein in PBMC subpopulations: CD3⁺, CD14⁺ and CD19⁺. The presence of virus and the proportion of affected cells within a particular PBMC fraction could indicate a principal target cell susceptible for HCV.

Methods

PBMC samples were collected from 26 treatment-free patients chronically infected with HCV. PBMC subpopulations: CD3⁺, CD14⁺, CD19⁺ were obtained using positive magnetic separation. The presence of negative strand RNA HCV and viral NS3 protein were analyzed by strand-specific RT-PCR and NS3 immunocytochemistry staining.

Results

Negative strand HCV RNA was detectable in 7/26 (27%), whereas NS3 protein in 15/26 (57.6%) of PBMC samples. At least one replication marker was found in 13/26 (50%) of CD3⁺ cells then in 8/26 (30.8%) of CD14⁺ and CD19⁺ cells. The highest percentage of cells harboring viral markers in single specimen was also observed in CD3⁺ (2.4%), then in CD19⁺ (1.2%), and much lower in CD14⁺ (0.4%) cells.

Conclusions

Our results indicate that CD3⁺ cells are a dominant site for extrahepatic HCV replication, although other PBMC subpopulations may also support virus replication.

A novel dengue virus inhibitor, BP13944, discovered by high-throughput screening with dengue virus replicon cells selects for resistance in the viral NS2B/NS3 protease

Dengue virus (DENV) causes disease globally, resulting in an estimated 25 to 100 million new infections per year. No effective DENV vaccine is available, and the current treatment is only supportive. Thus, there is an urgent need to develop therapeutic agents to cure this epidemic disease. In the present study, we identified a potential small-molecule inhibitor, BP13944, via high-throughput screening (HTS) of 60,000 compounds using a stable cell line harboring an efficient luciferase replicon of DENV serotype 2 (DENV-2). BP13944 reduced the expression of the DENV replicon reporter in cells, showing a 50% effective concentration (EC50) of 1.03 ± 0.09 μM. Without detectable cytotoxicity, the compound inhibited replication or viral RNA synthesis in all four serotypes of DENV but not in Japanese encephalitis virus (JEV). Sequencing analyses of several individual clones derived from BP13944-resistant RNAs purified from cells harboring the DENV-2 replicon revealed a consensus amino acid substitution (E66G) in the region of the NS3 protease domain. Introduction of E66G into the DENV replicon, an infectious DENV cDNA clone, and recombinant NS2B/NS3 protease constructs conferred 15.2-, 17.2-, and 3.1-fold resistance to BP13944, respectively. Our results identify an effective small-molecule inhibitor, BP13944, which likely targets the DENV NS3 protease. BP13944 could be considered part of a more effective treatment regime for inhibiting DENV in the future.

RNA dependent RNA polymerase of HCV: a potential target for the development of antiviral drugs

Hepatitis C virus (HCV) is a major cause of hepatocellular carcinoma, cirrhosis and end stage liver disease. More than 200million people are living with HCV worldwide with high morbidity and mortality. There is no vaccine available for this virus; the approved treatment option for the majority of HCV genotypes is the combination of pegylated (Peg) interferon and ribavirin. The therapy has a different response rate on different HCV genotypes and has a number of side effects. Recently, as well as Peg interferon and ribavirin, two protease inhibitors have been introduced to treat patients with HCV genotype 1 infection. The protease inhibitors have rapid onset of resistance and are not approved for use for infections with other HCV genotypes. The HCV NS5B gene encodes RNA dependent RNA polymerase (RdRp), which is the key player in viral replication and is a promising target for the development of antiviral drugs. HCV NS5B has been studied in various biochemical assays, cell based assays and animal model systems. So far, a number of nucleoside and non-nucleoside inhibitors have been screened for effects on viral replication. This review presents a deep insight into the structure and function of HCV polymerase and the effect of various nucleoside and non-nucleoside inhibitors on viral replication.

The HepaRG cell line: a valuable in vitro tool for hepatitis virus infection studies

Hepatitis virus infections, mainly hepatitis B virus (HBV) and hepatitis C virus (HCV) infections, constitute a major problem for public health since they have a worldwide distribution and because they are associated with hepatocellular carcinoma and death. Current anti-HBV vaccines seem to be effective in the majority of people. However, an important issue waiting to be tackled nowadays is how to cure patients with chronic hepatitis B. Moreover, no vaccine is available today for the prevention of HCV infection. Therefore, the use of adequate in vitro infection systems is a prerequisite for the molecular understanding of the infection events of these viruses, which could result in the development of novel powerful therapeutics. In this respect, the HepaRG cell line exhibits a hepatocyte-like morphology and displays drug metabolism capacity similar to that of primary hepatocytes. HepaRG cells have yet been proven to be a useful tool in the study of viral infections, particularly for deciphering the mechanism of HBV entry into hepatocytes.