A rapid and efficient method for studies of virus interaction at the host cell surface using enteroviruses and real-time PCR

Mouse Scarb2 Modulates EV-A71 Pathogenicity in Neonatal Mice

Enterovirus A71 (EV-A71) is a human pathogen that causes hand, foot, and mouth disease, which can progress to severe neurological disease. EV-A71 infects humans via the human scavenger receptor B2 (hSCARB2). It can also infect neonatal mice experimentally. Wild-type (WT) EV-A71 strains replicate primarily in the muscle of neonatal mice; however, susceptibility lasts only for a week after birth. Mouse-adapted (MA) strains, which can be obtained by serial passages in neonatal mice, are capable of infecting both muscle and neurons of the central nervous system. It is not clear how the host range and tropism of EV-A71 are regulated and why neonatal mice lose their susceptibility during development. We hypothesized that EV-A71 infection in neonatal mice is mediated by mouse Scarb2 (mScarb2) protein. Rhabdomyosarcoma (RD) cells expressing mScarb2 were prepared. Both WT and MA strains infected mScarb2-expressing cells, but the infection efficiency of the WT strain was much lower than that of the MA strain. Infection by WT and MA strains in vivo was abolished completely in Scarb2^-/- mice. Scarb2^+/- mice, in which Scarb2 expression was approximately half of that in Scarb2^+/+ mice, showed a milder pathology than Scarb2^+/+ mice after infection with the WT strain. The Scarb2 expression level in muscle decreased with aging, which was consistent with the reduced susceptibility of aged mice to infection. These results indicated that EV-A71 infection is mediated by mScarb2 and that the severity of the disease, the spread of virus, and the susceptibility period are modulated by mScarb2 expression. IMPORTANCE EV-A71 infects humans naturally but can also infect neonatal mice. The tissue tropism and severity of EV-A71 disease are determined by several factors, among which the virus receptor is thought to be important. We show that EV-A71 can infect neonatal mice using mScarb2. However, the infection efficiency of WT strains via mScarb2 is so low that an elevated virus-receptor interaction associated with mouse adaptation mutation and decrease in mScarb2 expression level during development modulate the severity of the disease, the spread of virus, and the susceptibility period in the artificial neonatal mice model.

Senescent endothelial cells are predisposed to SARS-CoV-2 infection and subsequent endothelial dysfunction

The coronavirus disease 2019 (COVID-19), caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), remains to spread worldwide. COVID-19 is characterized by the striking high mortality in elderly; however, its mechanistic insights remain unclear. Systemic thrombosis has been highlighted in the pathogenesis of COVID-19, and lung microangiopathy in association with endothelial cells (ECs) injury has been reported by post-mortem analysis of the lungs. Here, we experimentally investigated the SARS-CoV-2 infection in cultured human ECs, and performed a comparative analysis for post-infection molecular events using early passage and replicative senescent ECs. We found that; (1) SARS-CoV-2 infects ECs but does not replicate and disappears in 72 hours without causing severe cell damage, (2) Senescent ECs are highly susceptible to SARS-CoV-2 infection, (3) SARS-CoV-2 infection alters various genes expression, which could cause EC dysfunctions, (4) More genes expression is affected in senescent ECs by SARS-CoV-2 infection than in early passage ECs, which might causes further exacerbated dysfunction in senescent ECs. These data suggest that sustained EC dysfunctions due to SARS-CoV-2 infection may contribute to the microangiopathy in the lungs, leading to deteriorated inflammation and thrombosis in COVID-19. Our data also suggest a possible causative role of EC senescence in the aggravated disease in elder COVID-19 patients.

Angiotensin II Promotes SARS-CoV-2 Infection via Upregulation of ACE2 in Human Bronchial Cells

Blockers of the renin-angiotensin system (RAS) have been reported to increase the angiotensin converting enzyme (ACE)2, the cellular receptor of SARS-CoV-2, and thus the risk and course of COVID-19. Therefore, we investigated if angiotensin (Ang) II and RAS blockers affected ACE2 expression and SARS-CoV-2 infectivity in human epithelial bronchial Calu-3 cells. By infectivity and spike-mediated cell–cell fusion assays, we showed that Ang II acting on the angiotensin type 1 receptor markedly increased ACE2 at mRNA and protein levels, resulting in enhanced SARS-CoV-2 cell entry. These effects were abolished by irbesartan and not affected by the blockade of ACE-1-mediated Ang II formation with ramipril, and of ACE2- mediated Ang II conversion into Ang 1-7 with MLN-4760. Thus, enhanced Ang II production in patients with an activated RAS might expose to a greater spread of COVID-19 infection in lung cells. The protective action of Angiotensin type 1 receptor antagonists (ARBs) documented in these studies provides a mechanistic explanation for the lack of worse outcomes in high-risk COVID-19 patients on RAS blockers.

In vitro antiviral activity of peptide-rich extracts from seven Nigerian plants against three non-polio enterovirus species C serotypes

Background

As frequent viral outbreaks continue to pose threat to public health, the unavailability of antiviral drugs and challenges associated with vaccine development underscore the need for antiviral drugs discovery in emergent moments (endemic or pandemic). Plants in response to microbial and pest attacks are able to produce defence molecules such as antimicrobial peptides as components of their innate immunity, which can be explored for viral therapeutics.

Methods

In this study, partially purified peptide-rich fraction (P-PPf) were obtained from aqueous extracts of seven plants by reverse-phase solid-phase extraction and cysteine-rich peptides detected by a modified TLC method. The peptide-enriched fractions and the aqueous (crude polar) were screened for antiviral effect against three non-polio enterovirus species C members using cytopathic effect reduction assay.

Results

In this study, peptide fraction obtained from Euphorbia hirta leaf showed most potent antiviral effect against Coxsackievirus A13, Coxsackievirus A20, and Enterovirus C99 (EV-C99) with IC₅₀ < 2.0 µg/mL and selective index ≥ 81. EV-C99 was susceptible to all partially purified peptide fractions except Allamanda blanchetii leaf.

Conclusion

These findings establish the antiviral potentials of plants antimicrobial peptides and provides evidence for the anti-infective use of E. hirta in ethnomedicine. This study provides basis for further scientific investigation geared towards the isolation, characterization and mechanistic pharmacological study of the detected cysteine-rich peptides.

Accurate detection of Newcastle disease virus using proximity-dependent DNA aptamer ligation assays

Detecting viral antigens at low concentrations in field samples can be crucial for early veterinary diagnostics. Proximity ligation assays (PLAs) in both solution and solid‐phase formats are widely used for high‐performance protein detection in medical research. However, the affinity reagents used, which are mainly poly‐ and monoclonal antibodies, play an important role in the performance of PLAs. Here, we have established the first homogeneous and solid‐phase proximity‐dependent DNA aptamer ligation assays for rapid and accurate detection of Newcastle disease virus (NDV). NDV is detected by a pair of extended DNA aptamers that, upon binding in proximity to proteins on the envelope of the virus, are joined by enzymatic ligation to form a unique amplicon that can be sensitively detected using real‐time PCR. The sensitivity, specificity, and reproducibility of the assays were validated using 40 farm samples. The results demonstrated that the developed homogeneous and solid‐phase PLAs, which use NDV‐selective DNA aptamers, are more sensitive than the sandwich enzymatic‐linked aptamer assay (ELAA), and have a comparable sensitivity to real‐time reverse transcription PCR (rRT‐PCR) as the gold standard detection method. In addition, the solid‐phase PLA was shown to have a greater dynamic range with improved lower limit of detection, upper‐ and lower limit of quantification, and minimal detectable dose as compared with those of ELAA and rRT‐PCR. The specificity of PLA is shown to be concordant with rRT‐PCR.

Advances in high-throughput methods for the identification of virus receptors

Viruses have evolved many mechanisms to invade host cells and establish successful infections. The interaction between viral attachment proteins and host cell receptors is the first and decisive step in establishing such infections, initiating virus entry into the host cells. Therefore, the identification of host receptors is fundamental in understanding pathogenesis and tissue tropism. Furthermore, receptor identification can inform the development of antivirals, vaccines, and diagnostic technologies, which have a substantial impact on human health. Nevertheless, due to the complex nature of virus entry, the redundancy in receptor usage, and the limitations in current identification methods, many host receptors remain elusive. Recent advances in targeted gene perturbation, high-throughput screening, and mass spectrometry have facilitated the discovery of virus receptors in recent years. In this review, we compare the current methods used within the field to identify virus receptors, focussing on genomic- and interactome-based approaches.

Contemporary Circulating Enterovirus D68 Strains Have Acquired the Capacity for Viral Entry and Replication in Human Neuronal Cells

Since the EV-D68 outbreak during the summer of 2014, evidence of a causal link to a type of limb paralysis (AFM) has been mounting. In this article, we describe a neuronal cell culture model (SH-SY5Y cells) in which a subset of contemporary 2014 outbreak strains of EV-D68 show infectivity in neuronal cells, or neurotropism. We confirmed the difference in neurotropism in vitro using primary human neuron cell cultures and in vivo with a mouse paralysis model. Using the SH-SY5Y cell model, we determined that a barrier to viral entry is at least partly responsible for neurotropism. SH-SY5Y cells may be useful in determining if specific EV-D68 genetic determinants are associated with neuropathogenesis, and replication in this cell line could be used as rapid screening tool for identification of neurotropic EV-D68 strains. This may assist with better understanding of pathogenesis and epidemiology and with the development of potential therapies.

Enterovirus D68 (EV-D68) has historically been associated with respiratory illnesses. However, in the summers of 2014 and 2016, EV-D68 outbreaks coincided with a spike in polio-like acute flaccid myelitis/paralysis (AFM/AFP) cases. This raised concerns that EV-D68 could be the causative agent of AFM during these recent outbreaks. To assess the potential neurotropism of EV-D68, we utilized the neuroblastoma-derived neuronal cell line SH-SY5Y as a cell culture model to determine if differential infection is observed for different EV-D68 strains. In contrast to HeLa and A549 cells, which support viral infection of all EV-D68 strains tested, SH-SY5Y cells only supported infection by a subset of contemporary EV-D68 strains, including isolates from the 2014 outbreak. Viral replication and infectivity in SH-SY5Y were assessed using multiple assays: virus production, cytopathic effects, cellular ATP release, and VP1 capsid protein production. Similar differential neurotropism was also observed in differentiated SH-SY5Y cells, primary human neuron cultures, and a mouse paralysis model. Using the SH-SY5Y cell culture model, we determined that barriers to viral binding and entry were at least partly responsible for the differential infectivity phenotype. Transfection of genomic RNA into SH-SY5Y generated virions for all EV-D68 isolates, but only a single round of replication was observed from strains that could not directly infect SH-SY5Y. In addition to supporting virus replication and other functional studies, this cell culture model may help identify the signatures of virulence to confirm epidemiological associations between EV-D68 strains and AFM and allow for the rapid identification and characterization of emerging neurotropic strains.

A Single-Cell Platform for Monitoring Viral Proteolytic Cleavage in Different Cellular Compartments

Infectious diseases affect human health despite advances in biomedical research and drug discovery. Among these, viruses are especially difficult to tackle due to the sudden transfer from animals to humans, high mutational rates, resistance to current treatments, and the intricacies of their molecular interactions with the host. As an example of these interactions, we describe a cell-based approach to monitor specific proteolytic events executed by either the viral-encoded protease or by host proteins on the virus. We then emphasize the significance of examining proteolysis within the subcellular compartment where cleavage occurs naturally. We show the power of stable expression, highlighting the usefulness of the cell-based multiplexed approach, which we have adapted to two independent assays previously developed to monitor (a) the activity of the HIV-1-encoded protease or (b) the cleavage of the HIV-1-encoded envelope protein by the host. Multiplexing was achieved by mixing cells each carrying a different assay or, alternatively, by engineering cells expressing two assays. Multiplexing relies on the robustness of the individual assays and their clear discrimination, further enhancing screening capabilities in an attempt to block proteolytic events required for viral infectivity and spread.

Highly Sensitive Assay for Measurement of Arenavirus-cell Attachment

Arenaviruses are a family of enveloped RNA viruses that cause severe human disease. The first step in the arenavirus life cycle is attachment of viral particles to host cells. While virus-cell attachment can be measured through the use of virions labeled with biotin, radioactive isotopes, or fluorescent dyes, these approaches typically require high multiplicities of infection (MOI) to enable detection of bound virus. We describe a quantitative (q)RT-PCR-based assay that measures Junin virus strain Candid 1 attachment via quantitation of virion-packaged viral genomic RNA. This assay has several advantages including its extreme sensitivity and ability to measure attachment over a large dynamic range of MOIs without the need to purify or label input virus. Importantly, this approach can be easily tailored for use with other viruses through the use of virus-specific qRT-PCR reagents. Further, this assay can be modified to permit measurement of particle endocytosis and genome uncoating. In conclusion, we describe a simple, yet robust assay for highly sensitive measurement of arenavirus-cell attachment.

Effect of formaldehyde inactivation on poliovirus

Inactivated polio vaccines, which have been used in many countries for more than 50 years, are produced by treating live poliovirus (PV) with formaldehyde. However, the molecular mechanisms underlying virus inactivation are not well understood. Infection by PV is initiated by virus binding to specific cell receptors, which results in viral particles undergoing sequential conformational changes that generate altered structural forms (135S and 80S particles) and leads to virus cell entry. We have analyzed the ability of inactivated PV to bind to the human poliovirus receptor (hPVR) using various techniques such as ultracentrifugation, fluorescence-activated cell sorting flow cytometry and real-time reverse transcription-PCR (RT-PCR). The results showed that although retaining the ability to bind to hPVR, inactivated PV bound less efficiently in comparison to live PV. We also found that inactivated PV showed resistance to structural conversion in vitro, as judged by measuring changes in antigenicity, the ability to bind to hPVR, and viral RNA release at high temperature. Furthermore, viral RNA from inactivated PV was shown to be modified, since cDNA yields obtained by RT-PCR amplification were severely reduced and no infectious virus was recovered after RNA transfection into susceptible cells. Importance: This study represents a novel insight into the molecular mechanisms responsible for poliovirus inactivation. We show that inactivation with formaldehyde has an effect on early steps of viral replication as it reduces the ability of PV to bind to hPVR, decreases the sensitivity of PV to convert to 135S particles, and abolishes the infectivity of its viral RNA. These changes are likely responsible for the loss of infectivity shown by PV following inactivation. Techniques used in this study represent new approaches for the characterization of inactivated PV products and could be useful in developing improved methods for the production and quality control testing of inactivated polio vaccines. Measuring the antigenicity, capsid stability, and RNA integrity of inactivated PV samples could help establishing the optimal balance between the loss of infectivity and the preservation of virus antigenicity during inactivation.

Evaluation of RT-PCR and immunohistochemistry as tools for detection of enterovirus in the human pancreas and islets of Langerhans

BACKGROUND

Enteroviruses have been implicated in the etiology of type 1 diabetes, supported by immunoreactivity of enteroviral protein in islets, but presence of enteroviral genome has rarely been reported. Failure to detect enterovirus with RT-PCR has been attributed to the possible presence of PCR inhibitors and that only few cells are infected.

OBJECTIVES

The aim of this study was to evaluate strategies for detection of enterovirus in human islets.

STUDY DESIGN

A scenario was modeled with defined infected islets among a large number of uninfected pancreatic cells and the sensitivity of immunohistochemistry and PCR for detection of enterovirus was evaluated.

RESULTS

Enterovirus was detected with PCR when only one single human islet, infected in vitro with a low dose of virus, was mixed with an uninfected pancreatic biopsy. Enterovirus could not be detected by immunohistochemistry under the same conditions, demonstrating the superior sensitivity of PCR also in pancreatic tissue with only a small fraction of infected cells. In addition, we demonstrate that pancreatic cell culture supernatant does not cause degradation of enterovirus at 37°C, indicating that under normal culture conditions released virus is readily detectable. Utilizing PCR, the pancreases of two organ donors that died at onset of type 1 diabetes were found negative for enterovirus genome despite islet cells being positive using immunohistochemistry.

CONCLUSIONS

These data suggest that PCR should be the preferred screening method for enterovirus in the pancreas and suggest cautious interpretation of immunostaining for enterovirus that cannot be confirmed with PCR.

Characteristics of oncolytic vesicular stomatitis virus displaying tumor-targeting ligands

We sought proof of principle that tumor-targeting ligands can be displayed on the surface of vesicular stomatitis virus (VSV) by engineering its glycoprotein. Here, we successfully rescued VSVs displaying tumor vasculature-targeting ligands. By using a rational approach, we investigated various feasible insertion sites on the G protein of VSV (VSV-G) for display of tumor vasculature-targeting ligands, cyclic RGD (cRGD) and echistatin. We found seven sites on VSV-G that tolerated insertion of the 9-residue cRGD peptide, two of which could tolerate insertion of the 49-amino acid echistatin domain. All of the ligand-displaying viruses replicated as well as the parental virus. In vitro studies demonstrated that the VSV-echistatin viruses specifically bound to targeted integrins. Since the low-density lipoprotein receptor (LDLR) was recently identified as a major receptor for VSV, we investigated the entry of ligand-displaying viruses after masking LDLR. The experiment showed that the modified viruses can enter the cell independently of LDLR, whereas entry of unmodified virus is significantly blocked by a specific monoclonal antibody against LDLR. Both parental and ligand-displaying viruses displayed equal oncolytic efficacies in a syngeneic mouse myeloma model. We further demonstrated that single-chain antibody fragments against tumor-specific antigens can be inserted at the N terminus of the G protein and that corresponding replication-competent VSVs can be rescued efficiently. Overall, we demonstrated that functional tumor-targeting ligands can be displayed on replication-competent VSVs without perturbing viral growth and oncolytic efficacy. This study provides a rational foundation for the future development of fully retargeted oncolytic VSVs.

Antitumor potential of SLPI promoter controlled recombinant caspase-3 expression in laryngeal carcinoma

The purpose of this study is to develop a specific and efficient targeted gene therapy candidate approach for laryngeal carcinomas. Several promoters of human squamous cell carcinoma antigen 2(SCCA2), secretory leukocyte protease inhibitor (SLPI) and Survivin genes were cloned from human genomic DNA and evaluated for tumor-specific transcription potential in human laryngeal carcinoma Hep-2 cells by dual luciferase assays. One SLPI promoter fragment (677 bp) showed the highest efficiency and specificity, and was used to control the expression of a recombinant active caspases-3 (revCasp3), which could trigger apoptosis without activation of its upstream cascade elements once expressed in a cell, in an adenoviral vector (Ad-SLPI-revCasp3), and its antitumor efficacy was assessed. In vitro infection with Ad-SLPI-revCasp3 showed revCasp3 could be specifically expressed in Hep-2 cells, resulting in efficient activation of endogenous Caspase-3 and subsequent apoptosis of Hep-2 cells. In Hep-2 nude mice xenograft model, intratumoral administration of Ad-SLPI-revCasp3 significantly inhibited tumor growth without obvious loss of body weight and obvious hepatic toxicity. In summary, our study showed the specific and efficient apoptosis-inducing potential of Ad-SLPI-revCasp3, and this makes it a new candidate approach of targeted gene therapy for laryngeal squamous cell carcinoma, which needs further systematic investigation.

Comparison of an in-house real-time RT-PCR assay with a commercial assay for detection of enterovirus RNA in clinical samples

Molecular detection of enterovirus (EV) RNA based on PCR methods is a quicker and more sensitive approach than culture methods. At present, different PCR-based methods for EV RNA detection are available, but comparisons of results obtained according to the different approaches are limited. We evaluated an in-house real-time RT-PCR assay with a commercialized TaqMan real-time RT-PCR kit for detection of EV. Consecutive clinical specimens from paediatric patients less than 6 years old with clinical suspicion of EV infection were analyzed between July and November 2010. After RNA extraction, samples were amplified both by the real-time RT-PCR commercial assay and the in-house assay. A total of 19 of 132 patients (14.4%) involving 20 samples (14 plasma samples and 6 CSF) were positive in at least one of the two assays. The sensitivity of the in-house assay when the MutaPLATE® assay was used as a reference was 90% (IC 95%; 74.35-100) and the specificity was 100% (IC 95%; 99.63-100). Cts results of two methods were statistically correlated (r = 0.774; P = 0.01). In conclusion, these two real-time RT-PCR assays are rapid and easy methods for detection of EV.

Studies of Echovirus 5 interactions with the cell surface: heparan sulfate mediates attachment to the host cell

Infections caused by Echovirus 5 (E5), an enterovirus of the Picornaviridae family, have been associated with fever, rashes and sporadic cases of aseptic meningitis. To elucidate the receptor usage of this virus, the significance of a previously proposed integrin binding arginine-glycine-aspartic acid (RGD) motif found in the VP3 capsid protein was investigated, as well as the capacity of E5 to interact with heparan sulfate on the cell surface. Using the prototype strain E5 Noyce (E5N), an E5N mutant where the aspartic acid of the RGD motif has been substituted to a glutamic acid and clinical E5 isolates, the RGD motif of VP3 was found to be non-essential and hence not involved in integrin receptor binding. However, E5N and clinical E5 isolates interact with heparan sulfate at the cell surface, as demonstrated by virus replication inhibition assays using heparin and heparinase III, and studies of E5 interactions at the cell surface measured by real-time PCR analysis. In conclusion, E5 utilizes heparan sulfate as a cellular receptor, but the RGD motif of VP3 is not essential for E5 infectivity.