Characteristics and Functions of HEV Proteins

Multiple Functions of Hepatitis E Virus ORF3

Hepatitis E (Hepatitis E, HE) is an acute and chronic infectious hepatitis caused by hepatitis E virus (Hepatitis E Virus, HEV) infection, which is responsible for most acute hepatitis in the world and is a significant public health problem. The pathogen, HEV, has three Open Reading Frames (ORFs) ORF1, ORF2, and ORF3, each of which has a different function. Most of the current research is focused on ORF1 and ORF2, while the research on ORF3 is still relatively small. To provide more ideas for the study of HEV pathogenesis and the prevention and treatment of HE, this paper reviews the effects of ORF3 on the ERK pathway, growth factors, immune response, and virus release.

Effect and mechanism of C-terminal cysteine on the properties of HEV p222 protein

Preliminary investigations have demonstrated that the cysteines located at the C-terminus of HEV ORF2 protein exhibits disulfide bonding capability during virus-like particles (VLPs) assembly. However, the effect and mechanism underlying the pairing of disulfide bonds formed by C627, C630, and C638 remains unclear. The p222 protein encompasses C-terminus and serves as a representative of HEV ORF2 to investigate the specific impacts of C627, C630, and C638. The three cysteines were subjected to site-directed mutagenesis and expressed in prokaryotes; Both the mutated proteins and p222 underwent polymerization except for p222A; Surprisingly, only p222 was observed as abundant spherical particles under transmission electron microscope (TEM); Stability and immunogenicity of the p222 exhibited higher than other mutated proteins; LC/MS/MS analysis identified four disulfide bonds in the p222. The novel findings suggest that the three cysteines contribute to structural and functional properties of ORF2 protein, highlighting the indispensability of each cysteine.

Pathogenesis and clinical features of severe hepatitis E virus infection

The hepatitis E virus (HEV), a member of the Hepeviridae family, is a small, non-enveloped icosahedral virus divided into eight distinct genotypes (HEV-1 to HEV-8). Only genotypes 1 to 4 are known to cause diseases in humans. Genotypes 1 and 2 commonly spread via fecal-oral transmission, often through the consumption of contaminated water. Genotypes 3 and 4 are known to infect pigs, deer, and wild boars, often transferring to humans through inadequately cooked meat. Acute hepatitis caused by HEV in healthy individuals is mostly asymptomatic or associated with minor symptoms, such as jaundice. However, in immunosuppressed individuals, the disease can progress to chronic hepatitis and even escalate to cirrhosis. For pregnant women, an HEV infection can cause fulminant liver failure, with a potential mortality rate of 25%. Mortality rates also rise amongst cirrhotic patients when they contract an acute HEV infection, which can even trigger acute-on-chronic liver failure if layered onto pre-existing chronic liver disease. As the prevalence of HEV infection continues to rise worldwide, highlighting the particular risks associated with severe HEV infection is of major medical interest. This text offers a brief summary of the characteristics of hepatitis developed by patient groups at an elevated risk of severe HEV infection.

Hepatitis E Virus: An emerging enigmatic and underestimated pathogen

Hepatitis E virus (HEV) is an RNA virus causing hepatitis E disease. The virus is of one serotype but has diverse genotypes infecting both humans and animals. Based on evidence from seroprevalence studies, about 2 billion people are estimated to have been infected with HEV globally. HEV, therefore, poses a significant public health and economic challenge worldwide. HEV was discovered in the 1980s and was traced back to the 1955 - 1956 outbreak of hepatitis that occurred in India. Subsequently, several HEV epidemics involving thousands of individuals have occurred nearly annually in different countries in Asia and Africa. Initially, the virus was thought to be only enterically transmitted, and endemic in developing countries. Due to the environmental hygiene and sanitation challenges in those parts of the world. However, recent studies have suggested otherwise with the report of autochthonous cases in industrialised countries with no history of travel to the so-called endemic countries. Thus, suggesting that HEV has a global distribution with endemicity in both developing and industrialised nations. Studies have also revealed that HEV has multiple risk factors, and modes of transmission as well as zoonotic potentials. Additionally, recent findings have shown that HEV leads to severe disease, particularly among pregnant women. In contrast to the previous narration of a strictly mild and self-limiting infection. Studies have likewise demonstrated chronic HEV infection among immunocompromised persons. Consequent to these recent discoveries, this pathogen is considered a re - emerging virus, particularly in the developed nations. However, despite the growing public health challenges of this pathogen, the burden is still underestimated. The underestimation is often attributed to poor awareness among clinicians and a lack of routine checks for the disease in the hospitals. Thus, leading to misdiagnosis and underdiagnosis. Hence, this review provides a concise overview of epidemiology, diagnosis, and prevention of hepatitis E.

Interplay between Hepatitis E Virus and Host Cell Pattern Recognition Receptors

Hepatitis E virus (HEV) usually causes self-limiting acute hepatitis, but the disease can become chronic in immunocompromised individuals. HEV infection in pregnant women is reported to cause up to 30% mortality, especially in the third trimester. Additionally, extrahepatic manifestations like neuronal and renal diseases and pancreatitis are also reported during the course of HEV infection. The mechanism of HEV pathogenesis remains poorly understood. Innate immunity is the first line of defense triggered within minutes to hours after the first pathogenic insult. Growing evidence based on reverse genetics systems, in vitro cell culture models, and representative studies in animal models including non-human primates, has implicated the role of the host’s innate immune response during HEV infection. HEV persists in presence of interferons (IFNs) plausibly by evading cellular antiviral defense. This review summarizes our current understanding of recognizing HEV-associated molecular patterns by host cell Pattern Recognition Receptors (PRRs) in eliciting innate immune response during HEV infection as well as mechanisms of virus-mediated immune evasion.

Establishment of a Highly Sensitive Assay for Detection of Hepatitis E Virus-Specific Immunoglobulins

Hepatitis E, a liver disease caused by infection with the hepatitis E virus (HEV), is a worldwide emerging disease. The diagnosis is based on the detection of viral RNA and of HEV-specific immunoglobulins (Ig). For the latter, various assays are commercially available but still lack harmonization. In this study, a Luminex-based multiplex serological assay was established that measures the presence of total IgG, IgA, and IgM antibodies, targeting a short peptide derived from the viral E2 protein. For the validation, 160 serum samples with a known HEV serostatus were used to determine the assay cutoff and accuracy. Thereby, HEV IgG- and RNA-positive sera were identified with a sensitivity of 100% and a specificity of 98% (95% confidence interval [CI], 94% to 100%). Application of the assay by retesting 514 serum samples previously characterized with different HEV-IgG or total antibody tests revealed a high level of agreement between the assays (Cohen's kappa, 0.58 to 0.99). The established method is highly sensitive and specific and can be easily implemented in a multiplex format to facilitate rapid differential diagnostics with a few microliters of sample input.

The prevalence and genomic characteristics of hepatitis E virus in murine rodents and house shrews from several regions in China

Background

Urban rodents and house shrews are closely correlated in terms of location with humans and can transmit many pathogens to them. Hepatitis E has been confirmed to be a zoonotic disease. However, the zoonotic potential of rat HEV is still unclear. The aim of this study was to determine the prevalence and genomic characteristics of hepatitis E virus (HEV) in rodents and house shrews.

Results

We collected a total of 788 animals from four provinces in China. From the 614 collected murine rodents, 20.19% of the liver tissue samples and 45.76% of the fecal samples were positive for HEV. From the 174 house shrews (Suncus murinus), 5.17% fecal samples and 0.57% liver tissue samples were positive for HEV. All of the HEV sequences obtained in this study belonged to Orthohepevirus C1. However, we observed a lower percentage of identity in the ORF3 region upon comparing the amino acid sequences between Rattus norvegicus and Rattus losea. HEV derived from house shrews shared a high percentage of identity with rat HEV. Notably, the first near full-length of the HEV genome from Rattus losea is described in our study, and we also report the first near full-length rat HEV genomes in Rattus norvegicus from China.

Conclusion

HEV is prevalent among the three common species of murine rodents (Rattus. norvegicus, Rattus. tanezumi, and Rattus. losea) in China. HEV sequences detected from house shrews were similar to rat HEV sequences. The high identity of HEV from murine rodents and house shrews suggested that HEV can spread among different animal species.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1746-z) contains supplementary material, which is available to authorized users.

Effects of hepatitis E virus infection on interferon production via ISG15

AIM

To assess the effects of hepatitis E virus (HEV) on the production of type I interferons (IFNs) and determine the underlying mechanisms.

METHODS

We measured the production of interferon (IFN)-alpha and -beta (-α/β) in genotype 3 HEV-infected C3A cells at different time points (0, 8, 12, 24, 48, 72 and 120 h) by enzyme-linked immunosorbent assay (ELISA). The expression levels of IFN-stimulated gene (ISG)15 in HEV-infected C3A cells at different time points were tested by western blotting. The plasmid-expressing open reading frame 3 (ORF3) or control plasmids (green fluorescent protein-expressing) were transfected into C3A cells, and the levels of IFN-α/β and ISG15 were evaluated, respectively. Furthermore, the plasmid-expressing ISG15 or small interfering RNA-inhibiting ISG15 was transfected into infected C3A cells. Then, the production of IFN-α/β was also measured by ELISA.

RESULTS

We showed that genotype 3 HEV could enhance the production of IFN-α/β and induce elevation of ISG15 in C3A cells. HEV ORF3 protein could enhance the production of IFN-α/β and the expression of ISG15. Additionally, ISG15 silencing enhanced the production of IFN-α/β. Overexpression of ISG15 resulted in the reduction of IFN-α/β.

CONCLUSION

HEV may promote production of IFN-α/β and expression of ISG15 via ORF3 in the early stages, and increased ISG15 subsequently inhibited the production of IFN-α/β.

DESIGN OF HEPATITIS E VIRUS GENOTYPE 1 RECOMBINANT ORF3 PROTEIN BY CODON OPTIMIZATION METHOD

Aim. The development of the hepatitis E virus (HEV) genotype 1 full-size ORF3 recombinant polypeptide. Materials and methods. Escherichia coli strains, plasmid vectors, serological and clinical samples, ELISA reagent kits, molecular biological, bioinformatic, biotechnological, biochemical and serological methods. Results. HEV genotype 1 RNA had been isolated from clinical samples collected in Kyrgyzstan. DNA copy of subgenomic virus RNA had been cloned and used for further development of E.coli strains producing full-size recombinant protein ORF3 fused to E.coli beta-galactosidase. Codons optimization method was used in aim to increase expression level of recombinant protein. Recombinant protein ORF3 had been isolated from the inclusion bodies of the E.coli biomass and purified by size exclusion chromatography. Antigenic specificity of recombinant polypeptide had been confirmed by enzyme-linked immunosorbent assay and Western blotting with the specific sera. Conclusion. HEVgenotype 1 ORF3 recombinant antigen had been designed, and it’s applicability in diagnostic tests had been experimentally confirmed.