Targeting Cholesterol Metabolism as Efficient Antiviral Strategy Against the Hepatitis E Virus

Zika virus replication is impaired by a selective agonist of the TRPML2 ion channel

The flavivirus genus includes human pathogenic viruses such as Dengue (DENV), West Nile (WNV) and Zika virus (ZIKV) posing a global health threat due to limited treatment options. Ion channels are crucial for various viral life cycle stages, but their potential as targets for antivirals is often not fully realized due to the lack of selective modulators. Here, we observe that treatment with ML2-SA1, an agonist for the human endolysosomal cation channel TRPML2, impairs ZIKV replication. Upon ML2-SA1 treatment, levels of intracellular genomes and number of released virus particles of two different ZIKV isolates were significantly reduced and cells displayed enlarged vesicular structures and multivesicular bodies with ZIKV envelope protein accumulation. However, no increased ZIKV degradation in lysosomal compartments was observed. Rather, the antiviral effect of ML2-SA1 seemed to manifest by the compound's negative impact on genome replication. Moreover, ML2-SA1 treatment also led to intracellular cholesterol accumulation. ZIKV and many other viruses including the Orthohepevirus Hepatitis E virus (HEV) rely on the endolysosomal system and are affected by intracellular cholesterol levels to complete their life cycle. Since we observed that ML2-SA1 also negatively impacted HEV infections in vitro, this compound may harbor a broader antiviral potential through perturbing the intracellular cholesterol distribution. Besides indicating that TRPML2 may be a promising target for combatting viral infections, we uncover a tentative connection between this protein and cholesterol distribution within the context of infectious diseases.

Antagonism of epidermal growth factor receptor signaling favors hepatitis E virus life cycle

Hepatitis E virus (HEV) poses a global threat, which currently remains understudied in terms of host interactions. Epidermal growth factor receptor (EGFR) plays multifaceted roles in viral pathogenesis, impacting host-cell entry, viral replication, and host-defense modulation. On the one hand, EGFR signaling emerged as a major driver in innate immunity; on the other hand, a crosstalk between HEV and EGFR requires deeper analysis. We therefore aimed to dissect the receptor's involvement in the HEV life cycle. In persistently HEV-infected cells, the EGFR amount is decreased alongside with enhanced receptor internalization. As compared with the control ligand-induced EGFR, activation revealed an early receptor internalization and degradation in HEV-replicating cells, resulting in a notable EGFR signaling delay. Interestingly, inhibition or silencing of EGFR increased viral replication, extracellular and intracellular viral transcripts, and released infectious particles. The pro-viral impact of EGFR inhibition was attributed to (i) impaired expression of interferon-stimulated genes, (ii) activation of the autophagosomal system, (iii) virus-induced inhibition of lysosomal acidification, and (iv) a decrease of the cellular cholesterol level.

IMPORTANCE

This study identifies epidermal growth factor receptor (EGFR) as a novel host factor affecting hepatitis E virus (HEV): EGFR downregulation promotes viral replication, release, and evasion from the innate immune response. The discovery that EGFR inhibition favors viral spread is particularly concerning for HEV patients undergoing EGFR inhibitor treatment.

Sequestration of membrane cholesterol by cholesterol-binding proteins inhibits SARS-CoV-2 entry into Vero E6 cells

Membrane lipids and proteins form dynamic domains crucial for physiological and pathophysiological processes, including viral infection. Many plasma membrane proteins, residing within membrane domains enriched with cholesterol (CHOL) and sphingomyelin (SM), serve as receptors for attachment and entry of viruses into the host cell. Among these, human coronaviruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), use proteins associated with membrane domains for initial binding and internalization. We hypothesized that the interaction of lipid-binding proteins with CHOL in plasma membrane could sequestrate lipids and thus affect the efficiency of virus entry into host cells, preventing the initial steps of viral infection. We have prepared CHOL-binding proteins with high affinities for lipids in the plasma membrane of mammalian cells. Binding of the perfringolysin O domain four (D4) and its variant D4E458L to membrane CHOL impaired the internalization of the receptor-binding domain of the SARS-CoV-2 spike protein and the pseudovirus complemented with the SARS-CoV-2 spike protein. SARS-CoV-2 replication in Vero E6 cells was also decreased. Overall, our results demonstrate that the integrity of CHOL-rich membrane domains and the accessibility of CHOL in the membrane play an essential role in SARS-CoV-2 cell entry.

Cholesterol: A friend to viruses

Cholesterol is a key life-sustaining molecule which regulates membrane fluidity and serves as a signaling mediator. Cholesterol homeostasis is closely related to various pathological conditions including tumor, obesity, atherosclerosis, Alzheimer's disease and viral infection. Viral infection disrupts host cholesterol homeostasis, facilitating their own survival. Meanwhile, the host cells strive to reduce cholesterol accessibility to limit viral infection. This review focuses on the regulation of cholesterol metabolism and the role of cholesterol in viral infection, specifically providing an overview of cholesterol as a friend to promote viral entry, replication, assembly, release and immune evasion, which might inspire valuable thinking for pathogenesis and intervention of viral infection.

Broad-spectrum antiviral strategy: Host-targeting antivirals against emerging and re-emerging viruses

Viral infections are amongst the most prevalent diseases that pose a significant threat to human health. Targeting viral proteins or host factors represents two primary strategies for the development of antiviral drugs. In contrast to virus-targeting antivirals (VTAs), host-targeting antivirals (HTAs) offer advantages in terms of overcoming drug resistance and effectively combating a wide range of viruses, including newly emerging ones. Therefore, targeting host factors emerges as an extremely promising strategy with the potential to address critical challenges faced by VTAs. In recent years, extensive research has been conducted on the discovery and development of HTAs, leading to the approval of maraviroc, a chemokine receptor type 5 (CCR5) antagonist used for the treatment of HIV-1 infected individuals, with several other potential treatments in various stages of development for different viral infections. This review systematically summarizes advancements made in medicinal chemistry regarding various host targets and classifies them into four distinct catagories based on their involvement in the viral life cycle: virus attachment and entry, biosynthesis, nuclear import and export, and viral release.

The Protease Domain in HEV pORF1 Mediates the Replicase's Localization to Multivesicular Bodies and Its Exosomal Release

BACKGROUND

A peculiar feature of the hepatitis E virus (HEV) is its reliance on the exosomal route for viral release. Genomic replication is mediated via the viral polyprotein pORF1, yet little is known about its subcellular localization.

METHODS

Subcellular localization of pORF1 and its subdomains, generated and cloned based on a structural prediciton of the viral replicase, was analyzed via confocal laser scanning microscopy. Exosomes released from cells were isolated via ultracentrifugation and analyzed by isopycnic density gradient centrifugation. This was followed by fluorimetry or Western blot analyses or reverse transcriptase-polymerase chain reaction to analyze separated particles in more detail.

RESULTS

We found pORF1 to be accumulating within the endosomal system, most dominantly to multivesicular bodies (MVBs). Expression of the polyprotein's 7 subdomains revealed that the papain-like cysteine-protease (PCP) is the only domain localizing like the full-length protein. A PCP-deficient pORF1 mutant lost its association to MVBs. Strikingly, both pORF1 and PCP can be released via exosomes. Similarly, genomic RNA still is released via exosomes in the absence of pORF2/3.

CONCLUSIONS

Taken together, we found that pORF1 localizes to MVBs in a PCP-dependent manner, which is followed by exosomal release. This reveals new aspects of HEV life cycle, because replication and release could be coupled at the endosomal interface. In addition, this may mediate capsid-independent spread or may facilitate the spread of viral infection, because genomes entering the cell during de novo infection readily encounter exosomally transferred pORF1.

The activation of liver X receptors in Madin-Darby bovine kidney cells and mice restricts infection by bovine viral diarrhea virus

Bovine viral diarrhea virus (BVDV) is prevalent worldwide and is an important pathogen that represents a serious threat to the development of the cattle industry by causing significant economic losses. Liver X receptors (LXRs) are members of the nuclear receptor superfamily and have become attractive therapeutic targets for cardiovascular disease. In the present study, we found that LXRs in both Madin-Darby bovine kidney (MDBK) cells and mice were associated with BVDV infection. GW3965, an agonist for LXRs, significantly inhibited BVDV RNA and protein levels in MDBK cells. In vivo studies in a mouse model also confirmed the inhibitory role of GW3965 in BVDV replication and the ameliorating effect of GW3965 on pathological injury to the duodenum. In vitro investigations of the potential mechanisms involved showed that GW3965 significantly inhibited BVDV-induced increases in cholesterol levels and viral internalization. Furthermore, the antiviral activity of GW3965 was significantly reduced following cholesterol replenishment, thus demonstrating that cholesterol was involved in the resistance of GW3965 to BVDV replication. Further studies indicated the role of ATP-binding cassette transporter A1 (ABCA1) and cholesterol-25-hydroxylase (CH25H) in the antiviral activity of GW3965. We also demonstrated the significant antiviral effect of 25hydroxycholesterol (25HC), a product of the catalysis of cholesterol by CH25H. In addition, the anti-BVDV effects of demethoxycurcumin (DMC), cyanidin-3-O-glucoside (C3G), and saikosaponin-A (SSA), three natural agonizts of LXRs, were also confirmed in both MDBK cells and mice. However, the antiviral activities of these agents were weakened by SR9243, a synthetic inhibitor of LXRs. For the first time, our research demonstrated that the activation of LXRs can exert significant anti-BVDV effects in MDBK cells and mice.

Vital role of autophagy flux inhibition of placental trophoblast cells in pregnancy disorders induced by HEV infection

Hepatitis E virus (HEV) has become one of the important pathogens that threaten the global public health. Type 3 and 4 HEV are zoonotic, which can spread vertically and cause placental damage. At the same time, autophagy plays an important role in the process of embryo development and pregnancy maintenance. However, the relationship between HEV and autophagy, especially in the placenta tissue, has not been clarified. We found lower litter rates in HEV-infected female mice, with significant intrauterine abortion of the embryo (24.19%). To explore the effects of HEV infection on placenta autophagy, chorionic cells (JEG-3) and mice placenta have been employed as research objects, while the expression of autophagy-related proteins (ATGs) has been detected in JEG-3 cells with different times of HEV inoculation. The results demonstrated that the expression of protein LC3 decreased and p62 accumulated, meanwhile ATGs such as ATG4B, ATG5, and ATG9A in JEG-3 cells have decreased significantly. In addition, the maturation of autophagosomes, which referred to the process of the combination of autophagosomes and lysosomes was prevented by HEV infection as well. All processes of autophagic flux, which include the initiation, development, and maturation three stages, were suppressed in JEG-3 cells after HEV infection. Similarly, the protein and gene expression of LC3 were significantly decreased in the placenta of pregnant mice with HEV infection. In summary, our results suggested that HEV inhibited autophagy in JEG-3 cells and placenta of pregnant mice, which might be the important pathogenic mechanisms of HEV infection leading to embryo abortion.

25-hydroxycholesterol: an integrator of antiviral ability and signaling

Cholesterol, as an important component in mammalian cells, is efficient for viral entry, replication, and assembly. Oxysterols especially hydroxylated cholesterols are recognized as novel regulators of the innate immune response. The antiviral ability of 25HC (25-Hydroxycholesterol) is uncovered due to its role as a metabolic product of the interferon-stimulated gene CH25H (cholesterol-25-hydroxylase). With the advancement of research, the biological functions of 25HC and its structural functions have been interpreted gradually. Furthermore, the underlying mechanisms of antiviral effect of 25HC are not only limited to interferon regulation. Taken up by the special biosynthetic ways and structure, 25HC contributes to modulate not only the cholesterol metabolism but also autophagy and inflammation by regulating signaling pathways. The outcome of modulation by 25HC seems to be largely dependent on the cell types, viruses and context of cell microenvironments. In this paper, we review the recent proceedings on the regulatory effect of 25HC on interferon-independent signaling pathways related to its antiviral capacity and its putative underlying mechanisms.

Simulated dynamic cholesterol redistribution favors membrane fusion pore constriction

Endo- and exocytosis proceed through a highly strained membrane fusion pore topology regardless of the aiding protein machinery. The membrane's lipid components bias fusion pores toward expansion or closure, modifying the necessary work done by proteins. Cholesterol, a key component of plasma membranes, promotes both inverted lipid phases with concave leaflets (i.e., negative total curvature, which thins the leaflet) and flat bilayer phases with thick, ordered hydrophobic interiors. We demonstrate by theory and simulation that both leaflets of nascent catenoidal fusion pores have negative total curvature. Furthermore, the hydrophobic core of bilayers with strong negative Gaussian curvature is thinned. Therefore, it is an open question whether cholesterol will be enriched in these regions because of the negative total curvature or depleted because of the membrane thinning. Here, we compare all-atom molecular dynamics simulations (built using a procedure to create specific fusion pore geometries) and theory to understand the underlying reasons for lipid redistribution on fusion pores. Our all-atom molecular dynamics simulations resolve this question by showing that cholesterol is strongly excluded from the thinned neck of fusion and fission pores, revealing that thickness (and/or lipid order) influences cholesterol distributions more than curvature. The results imply that cholesterol exclusion can drive fusion pore closure by creating a small, cholesterol-depleted zone in the neck. This model agrees with literature evidence that membrane reshaping is connected to cholesterol-dependent lateral phase separation.

Augmentation of 3β-hydroxysteroid-Δ24 Reductase (DHCR24) Expression Induced by Bovine Viral Diarrhea Virus Infection Facilitates Viral Replication via Promoting Cholesterol Synthesis

Bovine viral diarrhea virus (BVDV) is the etiologic agent of bovine viral diarrhea-mucosal disease, one of the most important viral diseases of cattle, leading to numerous losses to the cattle rearing industry worldwide. The pathogenicity of BVDV is extremely complex, and many underlying mechanisms involved in BVDV-host interactions are poorly understood, especially how BVDV utilizes host metabolism pathway for efficient viral replication and spread. In our previous study, using an integrative analysis of transcriptomics and proteomics, we found that DHCR24 (3β-hydroxysteroid-Δ24 reductase), a key enzyme in regulating cholesterol synthesis, was significantly upregulated at both gene and protein levels in the BVDV-infected bovine cells, indicating that cholesterol is important for BVDV replication. In the present study, the effects of DHCR24-mediated cholesterol synthesis on BVDV replication was explored. Our results showed that overexpression of the DHCR24 effectively promoted cholesterol synthesis, as well as BVDV replication, while acute cholesterol depletion in the bovine cells by treating cells with methyl-β-cyclodextrin (MβCD) obviously inhibited BVDV replication. In addition, knockdown of DHCR24 (gene silencing with siRNA targeting DHCR24, siDHCR24) or chemical inhibition (treating bovine cells with U18666A, an inhibitor of DHCR24 activity and cholesterol synthesis) significantly suppressed BVDV replication, whereas supplementation with exogenous cholesterol to the siDHCR24-transfected or U18666A-treated bovine cells remarkably restored viral replication. We further confirmed that BVDV nonstructural protein NS5A contributed to the augmentation of DHCR24 expression. Conclusively, augmentation of the DHCR24 induced by BVDV infection plays an important role in BVDV replication via promoting cholesterol production. IMPORTANCE Bovine viral diarrhea virus (BVDV), an important pathogen of cattle, is the causative agent of bovine viral diarrhea-mucosal disease, which causes extensive economic losses in both cow- and beef-rearing industry worldwide. The molecular interactions between BVDV and its host are extremely complex. In our previous study, we found that an essential host factor 3β-hydroxysteroid-δ24 reductase (DHCR24), a key enzyme involved in cholesterol synthesis, was significantly upregulated at both gene and protein levels in BVDV-infected bovine cells. Here, we experimentally explored the function of the DHCR24-mediated cholesterol synthesis in regulating BVDV replication. We elucidated that the augmentation of the DHCR24 induced by BVDV infection played a significant role in viral replication via promoting cholesterol synthesis. Our data provide evidence that BVDV utilizes a host metabolism pathway to facilitate its replication and spread.

Interferon-induced transmembrane protein 3 (IFITM3) and its antiviral activity

Infections caused by enveloped viruses require fusion with cellular membranes for viral genome entry. Viral entry occurs following an interaction of viral and cellular membranes allowing the formation of fusion pores, by which the virus accesses the cytoplasm. Here, we focus on interferon-induced transmembrane protein 3 (IFITM3) and its antiviral activity. IFITM3 is predicted to block or stall viral fusion at an intermediate state, causing viral propagation to fail. After introducing IFITM3, we describe the generalized lipid membrane fusion pathway and how it can be stalled, particularly with respect to IFITM3, and current questions regarding IFITM3's topology, with specific emphasis on IFITM3's amphipathic α-helix (AAH) ₅₉V-₆₈M, which is necessary for the antiviral activity. We report new hydrophobicity and hydrophobic moment calculations for this peptide and a variety of active site peptides from known membrane-remodeling proteins. Finally, we discuss the effects of posttranslational modifications and localization, how IFITM3's AAH may block viral fusion, and possible ramifications of membrane composition.

Orsay Virus Infection of Caenorhabditis elegans Is Modulated by Zinc and Dependent on Lipids

Viruses utilize host lipids to promote the viral life cycle, but much remains unknown as to how this is regulated. Zinc is a critical element for life, and few studies have linked zinc to lipid homeostasis. We demonstrated that Caenorhabditis elegans infection by Orsay virus is dependent upon lipids and that mutation of the master regulator of lipid biosynthesis, sbp-1, reduced Orsay virus RNA levels by ~236-fold. Virus infection could be rescued by dietary supplementation with lipids downstream of fat-6/fat-7. Mutation of a zinc transporter encoded by sur-7, which suppresses the lipid defect of sbp-1, also rescued Orsay virus infection. Furthermore, reducing zinc levels by chemical chelation in the sbp-1 mutant also increased lipids and rescued Orsay virus RNA levels. Finally, increasing zinc levels by dietary supplementation led to an ~1,620-fold reduction in viral RNA. These findings provide insights into the critical interactions between zinc and host lipids necessary for virus infection. IMPORTANCE Orsay virus is the only known natural virus pathogen of Caenorhabditis elegans, which shares many evolutionarily conserved pathways with humans. We leveraged the powerful genetic tractability of C. elegans to characterize a novel interaction between zinc, lipids, and virus infection. Inhibition of the Orsay virus replication in the sbp-1 mutant animals, explained by the lipid depletion, can be rescued by a genetic and pharmacological approach that reduces the zinc accumulation and rescues the lipid levels in this mutant animal. Interestingly, the human ortholog of sbp-1, srebp-1, has been reported to play a role for virus infection, and zinc has been shown to inhibit the virus replication of multiple viruses. However, the mechanism through which zinc is acting is not well understood. These results suggest that the lipid regulation mediated by zinc may play a relevant role during mammalian virus infection.

Serological Evidence of Hepatitis B and E and Dengue Coinfection in Chadian Patients and Impact on Lipidemia Profile

OBJECTIVE

Viral hepatitis is an endemic disease in Chad. However, few studies have documented coinfection cases and their impact on cardiovascular risk. This study is aimed at analyzing hepatitis B, E and dengue coinfection in a Chadian cohort and gauge its effect on lipidemia. Patients and Methods. From February to May 2021, 179 subjects were recruited from the Department of Gastroenterology and Internal Medicine of the National Reference University Hospital of N'Djamena and tested for viral hepatitis markers, including HBsAg and IgM/IgG anti-HEV and dengue infection, using the NS1/IgM/IgG kit. Serum transaminases and biomarkers of lipid profiles were assayed by colorimetry, and atherogenic indexes (AI) and coronary risk (CRI) were calculated.

RESULTS

Of the 179 subjects surveyed, 21.22% (38/179) tested positive for hepatitis B, 20% (27/135) for hepatitis E, and 1.66% (2/120) for dengue. However, most of the patients were found to be asymptomatic. Hepatitis B/E coinfection was more frequent in the study population (5.02%; 9/179) than dengue/hepatitis E coinfection (0.83%; 1/120; IgM). The prevalence of anti-HEV IgG antibodies was higher (18.52%) than that of IgM (1.48%). Furthermore, IgG antibodies levels in HEV-monoinfected subjects (11.05 ± 1.93 IU/mL, N = 15) were significantly higher (p < 0.05) than in coinfected patients (5.40 ± 1.31 IU/mL, N = 9). Subjects coinfected with HEV/HBV were associated with a significantly higher risk of lipodystrophy (coronary risk: 88.89% vs. 35.3%, relative risk (RR) = 2.55; p = 0.014), than HEV-monoinfected subjects, as evidenced by higher mean levels of triglycerides levels (219.88 ± 14.67 mg/dL vs. 191.82 ± 4.66  mg/dL, p < 0.05), more reduced HDL-C levels (9.05 ± 1.62 mg/dL vs. 18.93 ± 2.35 mg/dL, p < 0.05), increased mean CRI (13.81 ± 2.39 vs. 6.89 ± 1.93, p < 0.01), and AI (1.46 ± 0.10 vs. 1.05 ± 0.05, p < 0.01) values. However, they had normal transaminase values and a lower risk of developing a liver injury, although not significant (alanine aminotransferase: 0% vs. 29.4%, RR = 1, p = 0.128; aspartate aminotransferase: 0% vs. 5.88%, p = 1) than this group.

CONCLUSION

HBV/HEV coinfection is frequent in the Chadian cohort and associated with an important risk of dyslipidemia. Further research is required to elucidate the mechanism of action.

Fenofibrate for COVID-19 and related complications as an approach to improve treatment outcomes: the missed key for Holy Grail

Introduction

Fenofibrate is an agonist of peroxisome proliferator activated receptor alpha (PPAR-α), that possesses anti-inflammatory, antioxidant, and anti-thrombotic properties. Fenofibrate is effective against a variety of viral infections and different inflammatory disorders. Therefore, the aim of critical review was to overview the potential role of fenofibrate in the pathogenesis of SARS-CoV-2 and related complications.

Results

By destabilizing SARS-CoV-2 spike protein and preventing it from binding angiotensin-converting enzyme 2 (ACE2), a receptor for SARS-CoV-2 entry, fenofibrate can reduce SARS-CoV-2 entry in human cells Fenofibrate also suppresses inflammatory signaling pathways, which decreases SARS-CoV-2 infection-related inflammatory alterations. In conclusion, fenofibrate anti-inflammatory, antioxidant, and antithrombotic capabilities may help to minimize the inflammatory and thrombotic consequences associated with SARSCoV-2 infection. Through attenuating the interaction between SARS-CoV-2 and ACE2, fenofibrate can directly reduce the risk of SARS-CoV-2 infection.

Conclusions

As a result, fenofibrate could be a potential treatment approach for COVID-19 control.

Viral Hepatitis, Cholesterol Metabolism, and Cholesterol-Lowering Natural Compounds

Hepatitis is defined as inflammation of the liver; it can be acute or chronic. In chronic cases, the prolonged inflammation gradually damages the liver, resulting in liver fibrosis, cirrhosis, and sometimes liver failure or cancer. Hepatitis is often caused by viral infections. The most common causes of viral hepatitis are the five hepatitis viruses—hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV), hepatitis D virus (HDV), and hepatitis E virus (HEV). While HAV and HEV rarely (or do not) cause chronic hepatitis, a considerable proportion of acute hepatitis cases caused by HBV (sometimes co-infected with HDV) and HCV infections become chronic. Thus, many medical researchers have focused on the treatment of HBV and HCV. It has been documented that host lipid metabolism, particularly cholesterol metabolism, is required for the hepatitis viral infection and life cycle. Thus, manipulating host cholesterol metabolism-related genes and proteins is a strategy used in fighting the viral infections. Efforts have been made to evaluate the efficacy of cholesterol-lowering drugs, particularly 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, in the treatment of hepatitis viral infections; promising results have been obtained. This review provides information on the relationships between hepatitis viruses and host cholesterol metabolism/homeostasis, as well as the discovery/development of cholesterol-lowering natural phytochemicals that could potentially be applied in the treatment of viral hepatitis.

Similarities, differences, and possible interactions between hepatitis E and hepatitis C viruses: Relevance for research and clinical practice

Hepatitis E virus (HEV) and hepatitis C virus (HCV) are both RNA viruses with a tropism for liver parenchyma but are also capable of extrahepatic manifestations. Hepatitis E is usually a viral acute fecal-oral transmitted and self-limiting disease presenting with malaise, jaundice, nausea and vomiting. Rarely, HEV causes a chronic infection in immunocompromised persons and severe fulminant hepatitis in pregnant women. Parenteral HCV infection is typically asymptomatic for decades until chronic complications, such as cirrhosis and cancer, occur. Despite being two very different viruses in terms of phylogenetic and clinical presentations, HEV and HCV show many similarities regarding possible transmission through organ transplantation and blood transfusion, pathogenesis (production of antinuclear antibodies and cryoglobulins) and response to treatment with some direct-acting antiviral drugs. Although both HEV and HCV are well studied individually, there is a lack of knowledge about coinfection and its consequences. The aim of this review is to analyze current literature by evaluating original articles and case reports and to hypothesize some interactions that can be useful for research and clinical practice.

Endosomal Cholesterol in Viral Infections - A Common Denominator?

Cholesterol has gained tremendous attention as an essential lipid in the life cycle of virtually all viruses. These seem to have developed manifold strategies to modulate the cholesterol metabolism to the side of lipid uptake and de novo synthesis. In turn, affecting the cholesterol homeostasis has emerged as novel broad-spectrum antiviral strategy. On the other hand, the innate immune system is similarly regulated by the lipid and stimulated by its derivatives. This certainly requires attention in the design of antiviral strategies aiming to decrease cellular cholesterol, as evidence accumulates that withdrawal of cholesterol hampers innate immunity. Secondly, there are exceptions to the rule of the abovementioned virus-induced metabolic shift toward cholesterol anabolism. It therefore is of interest to dissect underlying regulatory mechanisms, which we aimed for in this minireview. We further collected evidence for intracellular cholesterol concentrations being less important in viral life cycles as compared to the spatial distribution of the lipid. Various routes of cholesterol trafficking were found to be hijacked in viral infections with respect to organelle-endosome contact sites mediating cholesterol shuttling. Thus, re-distribution of cellular cholesterol in the context of viral infections requires more attention in ongoing research. As a final aim, a pan-antiviral treatment could be found just within the transport and re-adjustment of local cholesterol concentrations. Thus, we aimed to emphasize the importance of the regulatory roles the endosomal system fulfils herein and hope to stimulate research in this field.

Hepatitis E virus egress and beyond - the manifold roles of the viral ORF3 protein

Although the hepatitis E virus represents an uprising threat to the global community by representing the commonest cause of an acute viral hepatitis worldwide, its life cycle is grossly understudied. Albeit HEV is a non-enveloped virus, its progeny is released as quasi-enveloped virions. Thus, the responsible accessory protein pORF3 gained rising attention in the past years. It mediates viral release via the exosomal route by targeting the viral capsid to the endosomal system, more precisely to multivesicular bodies. As this is followed by quasi-envelopment, pORF3 may in terms represent a substitute to a conventional envelope protein. This feature proofs to be rather unique with respect to other enteric viruses, although the protein's role in the viral life cycle seems to reach far beyond simply maintaining release of progeny viruses. How pORF3 affects viral morphogenesis, how it mediates efficient viral release and how it supports viral spread is summarised in this microreview. With this, we aim to shed light on functions of pORF3 to gain further insights in still enigmatic aspects of the HEV life cycle. TAKE AWAYS: HEV is released as exosome via multivesicular bodies Viral pORF3 mediates release via endosomal complexes required for transport pORF3 modulates various cellular processes in infected cells Elucidation of pORF3-related processes imply novel clinical strategies.

Simvastatin Reduces Protection and Intestinal T Cell Responses Induced by a Norovirus P Particle Vaccine in Gnotobiotic Pigs

Noroviruses (NoVs) are a leading cause of acute gastroenteritis worldwide. P particles are a potential vaccine candidate against NoV. Simvastatin is a cholesterol-reducing drug that is known to increase NoV infectivity. In this study, we examined simvastatin’s effects on P particle-induced protective efficacy and T-cell immunogenicity using the gnotobiotic pig model of human NoV infection and diarrhea. Pigs were intranasally inoculated with three doses (100 µg/dose) of GII.4/VA387-derived P particles together with monophosphoryl lipid A and chitosan adjuvants. Simvastatin-fed pigs received 8 mg/day orally for 11 days prior to challenge. A subset of pigs was orally challenged with 10 ID₅₀ of a NoV GII.4/2006b variant at post-inoculation day (PID) 28 and monitored for 7 days post-challenge. Intestinal and systemic T cell responses were determined pre- and postchallenge. Simvastatin abolished the P particle’s protection and significantly increased diarrhea severity after NoV infection. Simvastatin decreased proliferation of virus-specific and non-specific CD8 T cells in duodenum and virus-specific CD4 and CD8 T cells in spleen and significantly reduced numbers of intestinal mononuclear cells in vaccinated pigs. Furthermore, simvastatin significantly decreased numbers of duodenal CD4+IFN-γ+, CD8+IFN-γ+ and regulatory T cells and total duodenal activated CD4+ and CD8+ T cells in vaccinated pigs pre-challenge at PID 28. Following challenge, simvastatin prevented the IFN-γ+ T cell response in spleen of vaccinated pigs. These results indicate that simvastatin abolished P particle vaccine-induced partial protection through, at least in part, impairing T cell immunity. The findings have specific implications for the development of preventive and therapeutic strategies against NoV gastroenteritis, especially for the elderly population who takes statin-type drugs.