Claudin-6 and Occludin Natural Variants Found in a Patient Highly Exposed but Not Infected with Hepatitis C Virus (HCV) Do Not Confer HCV Resistance In Vitro

Uncovering Resistance to Hepatitis C Virus Infection: Scientific Contributions and Unanswered Questions in the Irish Anti-D Cohort

Infections caused inadvertently during clinical intervention provide valuable insight into the spectrum of human responses to viruses. Delivery of hepatitis C virus (HCV)-contaminated blood products in the 70s (before HCV was identified) have dramatically increased our understanding of the natural history of HCV infection and the role that host immunity plays in the outcome to viral infection. In Ireland, HCV-contaminated anti-D immunoglobulin (Ig) preparations were administered to approximately 1700 pregnant Irish rhesus-negative women in 1977–1979. Though tragic in nature, this outbreak (alongside a smaller episode in 1993) has provided unique insight into the host factors that influence outcomes after HCV exposure and the subsequent development of disease in an otherwise healthy female population. Despite exposure to highly infectious batches of anti-D, almost 600 of the HCV-exposed women have never shown any evidence of infection (remaining negative for both viral RNA and anti-HCV antibodies). Detailed analysis of these individuals may shed light on innate immune pathways that effectively block HCV infection and potentially inform us more generally about the mechanisms that contribute to viral resistance in human populations.

The Expression of CLDN6 in Hepatocellular Carcinoma Tissue and the Effects of CLDN6 on Biological Phenotypes of Hepatocellular Carcinoma Cells

CLDN6, a member of claudin (CLDN) family, was found to be a breast cancer suppressor gene in our early experiments. However, CLDN6 was highly expressed in human hepatocellular carcinoma (hHCC) (TCGA database), and the role of CLDN6 in hHCC is still unclear. To investigate the expression of CLDN6, immunohistochemical staining was performed in hHCC tissues. As a result, hHCC tissues highly expressed CLDN6, and the expression was related to the degree of tumor's differentiation. To research the role of CLDN6 in hHCC cells, CLDN6 was silenced in HepG2 and Hep3B cells which highly expressed CLDN6 through liposome transfection. Results showed that after silencing of CLDN6, the proliferation, migration and invasion abilities of hHCC cells were inhibited. Meanwhile, the expression of E-cadherin was upregulated, and the expression of N-cadherin and Vimentin was downregulated. All the results above indicated that CLDN6 promoted the development of hHCC, and could be a potential target for the treatment of it.

A genome-wide association study on low susceptibility to hepatitis C virus infection (GEHEP012 study)

BACKGROUND

A low proportion of individuals repeatedly exposed to the hepatitis C virus (HCV) remain uninfected. This condition could have a genetic basis but it is not known whether or not it is mainly driven by a high-penetrance common allele.

OBJECTIVE

To explore whether low susceptibility to HCV infection is mainly driven by a high-penetrance common allele.

METHODS

In this genome-wide association study (GWAS), a total of 804 HCV-seropositive individuals and 27 high-risk HCV-seronegative (HRSN) subjects were included. Plink and Magma software were used to carry out single nucleotide polymorphism (SNP)-based and gene-based association analyses respectively.

RESULTS

No SNP nor any gene was associated with low susceptibility to HCV infection after multiple testing correction. However, SNPs previously associated with this trait and allocated within the LDLR gene, rs5925 and rs688, were also associated with this condition in our study under a dominant model (24 out of 27 [88.9%] rs5925-C carriers in the HRSN group vs 560 of 804 [69.6%] rs5925-C carriers in the HCV-seropositive group, P = 0.031, odds ratio [OR] = 3.48; 95% confidence interval [CI] = 1.04-11.58; and 24 out of 27 [88.9%] rs688-T carriers in the HRSN group vs 556 of 804 [69.1%] rs688-T carriers in the HCV-seropositive group, P = 0.028, OR = 3.57, 95% CI = 1.65-11.96).

CONCLUSIONS

Low susceptibility to HCV infection does not seem to be mainly driven by a high-penetrant common allele. By contrast, it seems a multifactorial trait where genes such as LDLR could be involved.

Role of the cytosolic domain of occludin in trafficking and hepatitis C virus infection

The role of the tight-junction (TJ) protein occludin (OCLN) in hepatitis C virus (HCV) entry remains elusive. Here, we investigated the OCLN C-terminal cytosolic domain in HCV infection. We expressed a series of C-terminal deletion mutants in Huh-7 cells KO for OCLN and characterized their functionality in HCV infection and trafficking. Deleting the OCLN cytosolic domain led to protein instability and intracellular retention. The first 15 residues (OCLN-C15 mutant) of the cytosolic domain were sufficient for OCLN stability, but led to its accumulation in the trans-Golgi network (TGN) due to a deficient cell surface export after synthesis. In contrast, the OCLN-C18 mutant, containing the first 18 residues of the cytosolic domain, was expressed at the cell surface and could mediate HCV infection. Point mutations in the context of C18 showed that I279 and W281 are crucial residues for cell surface expression of OCLN-C18. However, in the context of full-length OCLN, mutation of these residues only partially affected infection and cell surface localization. Importantly, the characterization of OCLN-C18 in human-polarized hepatocytes revealed a defect in its TJ localization without affecting HCV infection. These data suggest that TJ localization of OCLN is not a prerequisite for HCV infection in polarized hepatocytes.

Exploration of potential mechanisms of hepatitis C virus resistance in exposed uninfected intravenous drug users

A rare outcome following exposure to hepatitis C virus (HCV) is a lack of observable infection as clinically measured by HCV RNA- or HCV-recognizing antibodies. The population who exhibit this trait is termed exposed uninfected (EU). Increasing evidence has refined characterization of these individuals, distinct from those who become infected but spontaneously clear HCV. Study of the EU population is highly pertinent for the discovery of antiviral mechanisms of resistance that can reveal antiviral therapeutic strategies. This review provides an overview of similarities and differences of the EU population relative to spontaneous resolvers and the majority whom develop chronic HCV infection, and focusses on possible mechanisms of resistance including innate and adaptive immunity, genetics and lipid interactions.

Entry and Release of Hepatitis C Virus in Polarized Human Hepatocytes

Hepatitis C virus (HCV) primarily infects hepatocytes, which are highly polarized cells. The relevance of cell polarity in the HCV life cycle has been addressed only in distantly related models and remains poorly understood. Although polarized epithelial cells have a rather simple morphology with a basolateral and an apical domain, hepatocytes exhibit complex polarization structures. However, it has been reported that some selected polarized HepG2 cell clones can exhibit a honeycomb pattern of distribution of the tight-junction proteins typical of columnar polarized epithelia, which can be used as a simple model to study the role of cell polarization in viral infection of hepatocytes. To obtain similar clones, HepG2 cells expressing CD81 (HepG2-CD81) were used, and clones were isolated by limiting dilutions. Two clones exhibiting a simple columnar polarization capacity when grown on a semipermeable support were isolated and characterized. To test the polarity of HCV entry and release, our polarized HepG2-CD81 clones were infected with cell culture-derived HCV. Our data indicate that HCV binds equally to both sides of the cells, but productive infection occurs mainly when the virus is added at the basolateral domain. Furthermore, we also observed that HCV virions are released from the basolateral domain of the cells. Finally, when polarized cells were treated with oleic acid and U0126, a MEK inhibitor, to promote lipoprotein secretion, a higher proportion of infectious viral particles of lower density were secreted. This cell culture system provides an excellent model to investigate the influence of cell polarization on the HCV life cycle.IMPORTANCE Hepatitis C is a major health burden, with approximately 170 million persons infected worldwide. Hepatitis C virus (HCV) primarily infects hepatocytes, which are highly polarized cells with a complex organization. The relevance of cell polarity in the HCV life cycle has been addressed in distantly related models and remains unclear. Hepatocyte organization is complex, with multiple apical and basolateral surfaces. A simple culture model of HepG2 cells expressing CD81 that are able to polarize with unique apical and basolateral domains was developed to study HCV infection. With this model, we demonstrated that HCV enters and exits hepatocytes by the basolateral domain. Furthermore, lower-density viral particles were produced under conditions that promote lipoprotein secretion. This cell culture system provides a useful model to study the influence of cell polarization on HCV infection.

Qinggan Huoxue Recipe suppresses epithelial-to-mesenchymal transition in alcoholic liver fibrosis through TGF-β1/Smad signaling pathway

AIM: To investigate the mechanism by which Qinggan Huoxue Recipe (QGHXR) inhibits epithelial-to-mesenchymal transition (EMT) in rats with alcoholic liver fibrosis (ALF).

METHODS: A total of 75 male SD rats were used to induce ALF. Serum biochemical indicators, including alanine aminotransferase, aspartate aminotransferase, laminin and hyaluronidase, were measured. Liver histopathological changes were evaluated using hematoxylin-eosin and Sirius red staining. EMT was examined by analyzing the expression of the epithelial marker E-cadherin and the mesenchymal markers vimentin and fibronectin using RT-PCR and Western blot. The inhibitory effect of QGHXR on EMT markers, as well as its effect on molecules associated with the transforming growth factor (TGF)-β1/Smad signaling pathway, including TGF-β1, Smad3, snail, occludin, ZO-1 and claudin, was also examined.

RESULTS: Compared with normal control rats, ALF rats exhibited a decrease in E-cadherin levels (mRNA: ALF 0.16 ± 0.05 vs control 1.00 ± 0.08; protein: ALF 0.09 ± 0.05 vs control 0.70 ± 0.17, P < 0.01) and an increase in vimentin and fibronectin levels (mRNA: 11.43 ± 0.39 vs 1.00 ± 0.19 and 9.91 ± 0.34 vs 1.00 ± 0.44, respectively, P < 0.01; protein: 1.13 ± 0.42 vs 0.09 ± 0.03 and 1.16 ± 0.43 vs 0.09 ± 0.00, respectively, P < 0.01). This indicates that EMT occurred in ALF rats. In addition, the TGF-β1/Smad signaling pathway was activated in ALF rats, as evidenced by the increase in TGF-β1 and snail levels (mRNA: 1.76 ± 0.12 vs 1.00 ± 0.05 and 6.98 ± 0.41 vs 1.00 ± 0.10, respectively, P < 0.01; protein: 1.43 ± 0.05 vs 0.12 ± 0.03 and 1.07 ± 0.29 vs 0.07 ± 0.02, respectively, P < 0.01) and the decrease in Smad3 levels (mRNA: 0.05 ± 0.01 vs 1.00 ± 0.12, P < 0.01; protein: 0.06 ± 0.05 vs 0.89 ± 0.12, P < 0.01). Furthermore, levels of the tight junction markers occludin, ZO-1 and claudin decreased in ALF rats compared with healthy control rats (mRNA: 0.60 ± 0.09 vs 1.00 ± 0.12, 0.11 ± 0.00 vs 1.00 ± 0.12 and 0.60 ± 0.01 vs 1.00 ± 0.08, respectively, P < 0.01; protein: 0.05 ± 0.01 vs 0.87 ± 0.40, 0.09 ± 0.05 vs 0.89 ± 0.18 and 0.04 ± 0.03 vs 0.95 ± 0.21, respectively, P < 0.01). In ALF rats treated with QGHXR, E-cadherin levels increased (mRNA: QGHXR 0.67 ± 0.04 vs ALF model 0.16 ± 0.05, P < 0.01; protein: QGHXR 0.66 ± 0.21 vs ALF model 0.09 ± 0.05, P < 0.01), and vimentin and fibronectin levels decreased (mRNA: 6.57 ± 1.05 vs 11.43 ± 0.39 and 1.45 ± 1.51 vs 9.91 ± 0.34, respectively, P < 0.01; protein: 0.09 ± 0.03 vs 1.13 ± 0.42 and 0.10 ± 0.01 vs 1.16 ± 0.43, respectively, P < 0.01). In addition, QGHXR inhibited the expression of TGF-β1 and increased the expression of Smad3 (mRNA: 1.03 ± 0.11 vs 1.76 ± 0.12, 0.70 ± 0.10 vs 0.05 ± 0.01, respectively, P < 0.05 and P < 0.01; protein: 0.12 ± 0.03 vs 1.43 ± 0.05 and 0.88 ± 0.20 vs 0.06 ± 0.05, respectively, P < 0.01). QGHXR treatment also reduced the levels of the EMT-inducing transcription factor snail (mRNA: 2.28 ± 0.33 vs 6.98 ± 0.41, P < 0.01; protein: 0.08 ± 0.02 vs 1.07 ± 0.29, P < 0.01) and increased the occludin, ZO-1 and claudin levels (mRNA: 0.73 ± 0.05 vs 0.60 ± 0.09, 0.57 ± 0.04 vs 0.11 ± 0.00 and 0.68 ± 0.03 vs 0.60 ± 0.01, respectively, P < 0.01, P < 0.01 and P < 0.05; protein: 0.92 ± 0.50 vs 0.05 ± 0.01, 0.94 ± 0.22 vs 0.09 ± 0.05 and 0.94 ± 0.29 vs 0.04 ± 0.03, respectively, P < 0.01). The effects of QGR and HXR on the TGF-β1/Smad signaling pathway were similar to that of QGHXR; however, the QGR- and HXR-induced changes in vimentin mRNA levels, the QGR-induced changes in fibronectin mRNA levels and the HXR-induced changes in snail and TGF-β1 mRNA levels were not significant.

CONCLUSION: Qinggan Huoxue Recipe inhibits EMT in ALF rats by modulating the TGF-β1/Smad signaling pathway, suggesting that the mechanism underlying the amelioration of ALF induced by QGHXR is associated with this pathway.

Occludin-Knockout Human Hepatic Huh7.5.1-8-Derived Cells Are Completely Resistant to Hepatitis C Virus Infection

It is well known that occludin (OCLN) is involved in hepatitis C virus (HCV) entry into hepatocytes, but there has been no conclusive evidence that OCLN is essential for HCV infection. In this study, we first established an OCLN-knockout cell line derived from human hepatic Huh7.5.1-8 cells using the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 system, in which two independent targeting plasmids expressing single-guide RNAs were used. One established cell clone, named OKH-4, had the OCLN gene truncated in the N-terminal region, and a complete defect of the OCLN protein was shown using immunoblot analysis. Infection of OKH-4 cells with various genotypes of HCV was abolished, and exogenous expression of the OCLN protein in OKH-4 cells completely reversed permissiveness to HCV infection. In addition, using a co-culture system of HCV-infected Huh7.5.1-8 cells with OKH-4 cells, we showed that OCLN is also critical for cell-to-cell HCV transmission. Thus, we concluded that OCLN is essential for HCV infection of human hepatic cells. Further experiments using HCV genomic RNA-transfected OKH-4 cells or HCV subgenomic replicon-harboring OKH-4 cells suggested that OCLN is mainly involved in the entry step of the HCV life cycle. It was also demonstrated that the second extracellular loop of OCLN, especially the two cysteine residues, is critical for HCV infection of hepatic cells. OKH-4 cells may be a useful tool for understanding not only the entire mechanism of HCV entry, but also the biological functions of OCLN.