SARS-CoV-2 infection disrupts trophoblast function and placental syncytial barrier integrity via its accessory protein, ORF3a

Problem: Although it is rare for a SARS-CoV-2 infection to transmit vertically to the fetus during pregnancy, there is a significantly increased risk of adverse pregnancy outcomes due to maternalCOVID- 19. However, there is a poor understanding of such risks because mechanistic studies on how SARS-CoV-2 infection disrupts placental homeostasis are significantly lacking. The SARS-CoV-2 proteome includes multiple structural and non-structural proteins, including the non-structural accessory proteinORF3a. The roles of these proteins in mediating placental infection remain undefined. We and others have shown that autophagy activity in placental syncytium is essential for barrier function and integrity. Here, we have used clinical samples and cultured trophoblast cells to evaluate syncytial integrity of placenta exposed to SARS-CoV-2. The objective of our study was to investigate potential mechanisms through which SARS-CoV-2 impairs placental homeostasis and causes adverse pregnancy outcomes. We tested the central hypothesis that an essential SARS-CoV-2 non-structural and accessory protein, ORF3a, uniquely (amongst multiple viral proteins tested) with a novel three-dimensional structure andwith no homology to any other proteins is a key modulator of placental trophoblast cell dynamics via autophagy and intracellular trafficking of a tight junction protein (TJP), ZO-1. Method(s): We used clinical samples and cultured trophoblast cells to evaluate syncytial integrity of placentas exposed to SARS-CoV- 2. Autophagic flux was measured in placental villous biopsies from SARS-CoV-2-exposed and unexposed pregnant women by quantifying the expression of autophagy markers, LC3 and P62. Trophoblast cells (JEG-3, Forskolin-treated JEG-3, HTR8/SVneo, or primary human trophoblasts (PHTs)) were transfected with expression plasmids encoding SARS-CoV-2 proteins including ORF3a. Using western blotting, multi-label immunofluorescence, and confocal imaging, we analyzed the effect of ORF3a on the autophagy, differentiation, invasion, and intracellular trafficking of ZO-1 in trophoblasts. Using coimmunoprecipitation assays, we tested ORF3a interactions with host proteins. t-tests and one-way analyses of variance (ANOVAs) with post hoc tests were used to assess the data, with significance set at P < .05. Result(s): We discovered :1) increased activation of autophagy, but incomplete processing of autophagosome-lysosomal degradation;2) accumulation of protein aggregates in placentas exposed to SARS-CoV- 2. Mechanistically, we showed that the SARS-CoV-2 ORF3a protein, uniquely 3) blocks the autophagy-lysosomal degradation process;4) inhibits maturation of cytotrophoblasts into syncytiotrophoblasts (STBs);5) reduces production ofHCG-beta, a key pregnancy hormone that is also essential for STB maturation;and 6) inhibits trophoblast invasive capacity. Furthermore, ORF3a harbors an intrinsically disordered C-terminus withPDZ-bindingmotifs.We show for the first time that, 7) ORF3a binds to and co-localizes with the PDZ domain of ZO-1, a junctional protein that is essential for STB maturation and the integrity of the placental barrier. Conclusion(s): Our work outlines a new molecular and cellular mechanism involving the SARS-CoV-2 accessory protein ORF3a that may drive the virus's ability to infect the placenta and damage placental syncytial integrity. This implies that the mechanisms facilitating viral maturation, such as the interaction of ORF3a with host factors, can be investigated for additional functionality and even targeted for developing new intervention strategies for treatment or prevention of SARS-CoV-2 infection at the maternal-fetal interface.

Identification of small molecules capable of enhancing viral membrane fusion.

Several approaches have been developed to analyze the entry of highly pathogenic viruses. In this study, we report the implementation of a Bimolecular Multicellular Complementation (BiMuC) assay to safely and efficiently monitor SARS-CoV-2 S-mediated membrane fusion without the need for microscopy-based equipment. Using BiMuC, we screened a library of approved drugs and identified compounds that enhance S protein-mediated cell-cell membrane fusion. Among them, ethynylestradiol promotes the growth of SARS-CoV-2 and Influenza A virus in vitro. Our findings demonstrate the potential of BiMuC for identifying small molecules that modulate the life cycle of enveloped viruses, including SARS-CoV-2.

SARS-CoV-2 BA.5 CAUSES HIGHER REPLICATION AND LETHAL INFECTION IN K18-hACE2 MICE

Background: The continuous evolution of SARS-CoV-2 in the diverse immune landscape (natural, vaccine, hybrid) is giving rise to novel immune escape mutations. So far, the resulting new variants (BA.1, BA.2, BA.2.12.1) were observed to cause mild infections, however, BA.5 infections are associated with an increased risk of hospitalization.1 Therefore it is essential to investigate the pathogenesis of BA.5. Method(s): Here we compared the pathogenicity of Pre-Omicron (B.1.351) and Omicron (BA.1, BA.2.12.1, and BA.5) variants in wild-type C57BL/6J mice and K18-hACE2 mice. The virus replication kinetics was also studied in human Calu3, pulmonary alveolar type 2 (AT2) cells, and airway organoids (HAO). Cell-to-cell spread of virus was measured by syncytia formation assay and immunohistochemistry (IHC) of infected lungs. Result(s): In the results, infection in C57BL/6J mice showed severe weight loss ( >15%) for B.1.351 infected mice and moderate ( >5%) for BA.5 infected. C57BL/6J mice showed higher virus replication of B.1.351 followed by BA.5, BA.1, and BA.2.12.1. At the peak of virus replication (2 days) plaque-forming units from lung extract of BA.5 infected mice were two, and three logs higher compared to BA.1 and BA.2.12.1 respectively. BA.5 infection was lethal to 80% of infected K18-hACE2 mice, whereas the mice looked normal after infection with BA.1 and BA.2.12.1. BA.5 infected mice showed high virus replication in brain tissue. Surprisingly the syncytia formation assay and IHC for BA.5 was comparable to that of B.1.351, indicating the higher cell-to-cell spread of BA.5 and B.1.351 compared to BA.1 and BA.2.12.1, which is one of the measures of pathogenicity. Calu3 and HAO showed the same trend of virus replication as was observed in-vivo experiments however AT2 cells were found to be resistant to BA.5 replication. Conclusion(s): These results suggest that the BA.5 variant (lineage) of Omicron has the potential to regain the pathogenicity as it shows increased virulence compared to other Omicron sub-variants. Lethal infection of BA.5 in K18-hACE2 mice may be attributed to catastrophic encephalitis and increased cell-to-cell spread.

Fc RECEPTOR-MEDIATED INFECTION OF MYELOID CELLS BY SARS-CoV-2

Background: The role of myeloid cells in the pathogenesis of SARS-CoV-2 is well established, in particular as drivers of cytokine production and systemic inflammation characteristic of severe COVID-19. However, the potential for myeloid cells to act as bona fide targets of productive SARS-CoV-2 infection remains unclear. Method(s): Using anti-SARS-CoV-2 mAbs with a range of neutralisation potencies and binding specificities, we performed a detailed assessment of mAb-mediated infection of monocytes/macrophages. THP-1 cells were used as a model system, with results confirmed in primary macrophages. Result(s): Infection of THP-1 cells was seen via mAbs targeting the spike RBD, but not with those targeting the NTD or S2 subunit. mAbs with the most consistent potential to mediate infection targeted a conserved region of the RBD (group 1/class IV). No infection was seen with the same quantity of virus but in the absence of antibody, and pre-treating the cells with FcgammaRI and -II blocking antibodies inhibited infection. Thus, antibody-FcR interactions are able to expand the tropism of SARS-CoV-2. Time-course studies demonstrated high-level and productive infection. Studies performed in human iPSC-derived macrophages and primary monocyte-derived macrophages paralleled results seen in THP-1 cells but with lower infection levels. Up to 2% of macrophages were infected, with infected cells appearing multinucleated and syncytial. Addition of ruxolitinib, an inhibitor of JAK1/2 signalling, increased infection up to 10-fold, indicating limitation of infection through innate immune mechanisms. Sera from primary infections (n=80) mediated rare infection events, with a minority of samples (n=3) promoting significant infection. Competition assays confirmed results seen in sera, with the addition of neutralising mAbs diminishing the infection seen with infection-mediating mAbs. Thus, the presence of antibodies with potential to mediate infection is not sufficient to predict myeloid cell infection, rather, the context in which the antibodies are produced is key. Conclusion(s): We hypothesise that a nascent antibody response during peak viral replication in primary infection presents a window of opportunity for myeloid cells to become infected, while establishment of a robust polyclonal response via vaccination or prior infection reduces the likelihood of this occurring. Infection via antibody-FcR interactions could contribute to pathogenesis in primary infection, systemic virus spread or persistent infection.

NK CELLS ARE CRITICAL FOR IN VIVO CONTROL OF SARS-CoV-2 REPLICATION AND DISEASE

Background: Natural killer (NK) cells play a critical role in control of viral infections. However, empirical evidence thus far has been unclear on the role of NK cells in pathogenesis and control of SARS-CoV-2 infection with some research suggesting NK cell accumulation as beneficial while others indicate it as deleterious. To address this crucial deficit in understanding, we employed a non-human primate infection model with a validated experimental NK cell depletion technique. Method(s): A total of 12 experimentally naive (75% female) cynomolgus macaques (CM) of Cambodian origin were used in this study. Six CM were NK cell-depleted using an anti-IL-15 neutralizing antibody, while six controls received placebo, prior to intranasal and intratracheal challenge with the SARS-CoV-2 Delta variant at a TCID50 of 1X105. The cohort was monitored for five weeks with scheduled blood, colorectal (CR) biopsies, and lymph node (LN) collections. Total envelope and sub-genomic viral loads (VL) were measured in the nasal cavity, throat, and bronchoalveolar lavage (BAL). 23-color flow cytometry, pathology, and 27-plex inflammatory analyte Luminex analyses were conducted. Statistical tests used were Mann-Whitney U and Spearman's Correlation. Result(s): Control CM exhibited an increase in the frequency of circulating NK cells, reaching a peak at 10 days post-infection (DPI) and returning to baseline by 22DPI. Simultaneously, NK cells expressing activation and tissue retention marker, CD69, also significantly increased. Cytotoxic NK cells were positively associated with VL (r=0.66;p=0.02), suggestive of a virus-induced mobilization. Total experimental NK cell ablation was verified in blood, CR, and LN of NK celldepleted CM, which had higher VL compared to controls in all tissues evaluated, reaching significance at 10DPI (p=0.01) and demonstrated a longer duration of viremia. Although Luminex measures were similar in plasma, BAL samples from NK cell-depleted CM had universally higher concentrations of inflammatory mediators, most notably a 25-fold higher concentration of IFN-alpha compared to controls. Lung pathology scores were also higher in NK cell-depleted CM with increased evidence of fibrosis, syncytia, pneumocyte hyperplasia, and endothelialitis. Conclusion(s): Overall, we find significant and conclusive evidence for NK cell-mediated control of SARS-CoV-2 virus replication and disease pathology. These data suggest adjunct therapies for infection could largely benefit from NK cell-targeted approaches.

Human airway and nasal organoids reveal escalating replicative fitness of SARS-CoV-2 emerging variants.

The high transmissibility of SARS-CoV-2 Omicron subvariants was generally ascribed to immune escape. It remained unclear whether the emerging variants have gradually acquired replicative fitness in human respiratory epithelial cells. We sought to evaluate the replicative fitness of BA.5 and earlier variants in physiologically active respiratory organoids. BA.5 exhibited a dramatically increased replicative capacity and infectivity than B.1.1.529 and an ancestral strain wildtype (WT) in human nasal and airway organoids. BA.5 spike pseudovirus showed a significantly higher entry efficiency than that carrying WT or B.1.1.529 spike. Notably, we observed prominent syncytium formation in BA.5-infected nasal and airway organoids, albeit elusive in WT- and B.1.1.529-infected organoids. BA.5 spike-triggered syncytium formation was verified by lentiviral overexpression of spike in nasal organoids. Moreover, BA.5 replicated modestly in alveolar organoids, with a significantly lower titer than B.1.1.529 and WT. Collectively, the higher entry efficiency and fusogenic activity of BA.5 spike potentiated viral spread through syncytium formation in the human airway epithelium, leading to enhanced replicative fitness and immune evasion, whereas the attenuated replicative capacity of BA.5 in the alveolar organoids may account for its benign clinical manifestation.

Impact of the COVID-19 pandemic on the seasonality of respiratory syncytial viral infection.

The article presents an overview of current trends in the epidemiology of respiratory syncytial viral (RSV) infection, including its seasonality, under the impact of the COVID-19 pandemic, both according to world literature and taking into account monitoring epidemiological studies conducted in the Russian Federation. A detailed description of the dynamics of RSV detection in the period 2020-2021 and the beginning of 2022 in Russia according to the results of the all-Russian epidemiological monitoring is given. Epidemiological studies in different regions of the world, including Russia, have revealed the absence of seasonal rises in the incidence of RSV infection, characteristic of previous years, in 2020 and winter-spring in 2021 under the influence of the COVID-19 pandemic. In 2021-2022, a sharp increase in the incidence and hospitalization of children was noted against the backdrop of a decrease in cases of a new coronavirus infection in all countries of the world, while the start time and duration of respiratory syncytial virus infection, typical for the prepandemic period, changed. Our previous studies have shown that in different years and in different regions of Russia, the start and end times of the epidemiological season may also not coincide, which makes it difficult to predict seasonal peaks in incidence, their duration and severity only on the basis of previously obtained data. This makes it expedient to extend the terms of passive specific prophylaxis with palivizumab for a year if there are indications for its use, including taking into account the data of epidemiological monitoring conducted in the Russian Federation.Copyright © 2022 Authors. All rights reserved.

Astersaponin I from Aster koraiensis is a natural viral fusion blocker that inhibits the infection of SARS-CoV-2 variants and syncytium formation.

The continuous emergence of SARS-CoV-2 variants prolongs COVID-19 pandemic. Although SARS-CoV-2 vaccines and therapeutics are currently available, there is still a need for development of safe and effective drugs against SARS-CoV-2 and also for preparedness for the next pandemic. Here, we discover that astersaponin I (AI), a triterpenoid saponin in Aster koraiensis inhibits SARS-CoV-2 entry pathways at the plasma membrane and within the endosomal compartments mainly by increasing cholesterol content in the plasma membrane and interfering with the fusion of SARS-CoV-2 envelope with the host cell membrane. Moreover, we find that this functional property of AI as a fusion blocker enables it to inhibit the infection with SARS-CoV-2 variants including the Alpha, Beta, Delta, and Omicron with a similar efficacy, and the formation of syncytium, a multinucleated cells driven by SARS-CoV-2 spike protein-mediated cell-to-cell fusion. Finally, we claim that the triterpene backbone as well as the attached hydrophilic sugar moieties of AI are structurally important for its inhibitory activity against the membrane fusion event. Overall, this study demonstrates that AI is a natural viral fusion inhibitor and proposes that it can be a broad-spectrum antiviral agent against current COVID-19 pandemic and future outbreaks of novel viral pathogens.

Nanoluciferase-based cell fusion assay for rapid and high-throughput assessment of SARS-CoV-2-neutralizing antibodies in patient samples.

After more than two years, COVID-19 still represents a global health burden of unprecedented extent and assessing the degree of immunity of individuals against SARS-CoV-2 remains a challenge. Virus neutralization assays represent the gold standard for assessing antibody-mediated protection against SARS-CoV-2 in sera from recovered and/or vaccinated individuals. Neutralizing antibodies block the interaction of viral spike protein with human angiotensin-converting enzyme 2 (ACE2) receptor in vitro and prevent viral entry into host cells. Classical viral neutralization assays using full replication-competent viruses are restricted to specific biosafety level 3-certified laboratories, limiting their utility for routine and large-scale applications. We developed therefore a cell-fusion-based assay building on the interaction between viral spike and ACE2 receptor expressed on two different cell lines, substantially reducing biosafety risks associated with classical viral neutralization assays. This chapter describes this simple, sensitive, safe and cost-effective approach for rapid and high-throughput evaluation of SARS-CoV-2 neutralizing antibodies relying on high-affinity NanoLuc® luciferase complementation technology (HiBiT). When applied to a variety of standards and patient samples, this method yields highly reproducible results in 96-well, as well as in 384-well format. The use of novel NanoLuc® substrates with increased signal stability like Nano-Glo® Endurazine™ furthermore allows for high flexibility in assay set-up and full automatization of all reading processes. Lastly, the assay is suitable to evaluate the neutralizing capacity of sera against the existing spike variants, and potentially variants that will emerge in the future.

The Impact of COVID-19 Pandemic Social Distancing and Mask Mandates on the Prevalence of Influenza and RSV During Their Peak Season

Background: Influenza and bronchiolitis are serious infections especially among vulnerable pediatric populations. Earlier studies have suggested that the transmission of influenza viruses can be reduced by face masking and social distancing measures. In response to the COVID-19 pandemic, Ohio adopted various measures including school closing, travel restrictions, social distancing, and face masking in March, 2020. These measures have created a unique opportunity to study the impact of social distancing measures on the spread of potentially serious viral infections such as influenza and respiratory syncytial viral (RSV) infections of children in our locality. Methods: This is a retrospective cohort study conducted at Akron Children's hospital in Northeast Ohio where the peak respiratory season extends from October to April. The primary outcome was to evaluate the prevalence of influenza A and B and RSV infections before and after implementation of social distancing measures. Prevalence of SARS-CoV-2 was also tracked for comparison. Viral assay data were collected between October 1, 2020 through April 30th, 2021 (during the pandemic and social distancing implementation) and compared with two pre-COVID19 respiratory seasons: 2018-19 and 2019-20. Results from all patients who received viral testing as a part of their medical care were included. Viral tests included rapid antigen tests for Influenza A/B and RSV (Quidel SoFIA), Respiratory Film Array (BioFire, includes flu, RSV, and SARS-CoV-2 targets), and single target tests for SARS-CoV-2 from multiple vendors (see Table 1). Results: There was a dramatic increase in viral testing in the 2020-2021 respiratory season. With most of the new test targeting SARS-CoV-2, Flu and RSV antigen tests decreased significantly but were replaced in part by Respiratory FilmArray use (Table 1). Pre-COVID-19, the peak incidence of RSV occurred in December for the 2018-19 (28.9%, average of 8.8%) and 2019- 20 (24.7%, average of 8.8%) seasons. After social distancing measures, the incidence and positivity rate for RSV was 0% until March 14, 2021 when the first RSV case was detected in our locality, concurrent with relaxation of social distancing measures. Pre-COVID 19, the peak incidence of Influenza A virus occurred during February in the seasons 2018-19 (40.9%;average of 13.6%) and 2019-20 (24.1%, average of 6.1%). Influenza B had a low incidence throughout 2018-2019 (average of 0.3%) with a peak during January in the 2019-2020 season (24.0%, average of 6.8%). During the 2020-2021 season, we detected only two isolated cases of Influenza B virus and no cases of Influenza A virus through April 30, 2021 (Figure-1). Conclusion: Social distancing and mask mandates can be effective tools to decrease the rates of potentially serious infections such as Influenza and RSV in the pediatric population. Travel restrictions and school closures likely had an affect but were not evaluated during this study.

EXPRESSION OF EPITHELIAL PROTEASES PREDICTS SARS-COV-2 ENTRY IN HUMAN ENTEROIDS

Introduction: Coronavirus Disease 2019 (COVID-19) is an ongoing public health crisis that has sickened or precipitated death in millions. The etiologic agent of COVID-19, Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), infects the intestinal epithelium and can persist long after the respiratory infection has cleared. We previously observed that intestinal SARS-CoV-2 infection levels varied by individual donors and did not correlate positively with ACE2, the cognate SARS-CoV-2 receptor. Therefore we aimed to delineate host factors that influence viral infection in the intestine. Methods: Published dataset GSE75214 was downloaded and expression levels of select genes were querried. Primary human ileal spheroids (enteroids), derived from healthy donors and patients with Crohn's disease (CD), were grown on 2D transwells until confluent. Cells were differentiated for 3d before infection with a modified vesicular stomatitis virus expressing the SARS-CoV-2 spike protein (VSV-SARS-CoV-2) and GFP for 1h at a multiplicity of infection of ~0.5. Cells were harvested pre-infection and 24h after infection and expression of select genes was performed by qRT-PCR. Expression data were fit to a linear regression model to predict viral RNA levels. Results: Small intestine biopsy samples from CD patients demonstrated a reduction in ACE and an increase in CTSB and CTSL expression during active inflammation compared to healthy controls. Viral RNA expression did not correlate with ACE2 expression in CD enteroids. A subset of CD enteroids exhibited enhanced protease expression (TMPRSS2, TMPRSS4, CTSL), each of which correlated with higher viral RNA levels (P=0.04, P=0.002, P=0.006, respectively). Expression of these proteases was higher in the pre-infection for the sample subset. Principle component analysis of uninfected expression data demonstrated these samples clustered separately from the others, with the difference driven by TMPRSS2, TMPRSS4, and CTSL. Modeling viral RNA levels based on gene expression revealed expression levels of these proteases are a predictive expression signature. Conclusions: Host protease expression can predict SARS-CoV-2 infection and represent potential therapeutic targets for COVID-19. This is consistent with the recent report showing that cathepsin inhibition reduces SARS-CoV-2 spike-mediated syncytia formation. High expression of these proteases in the intestine may also be a novel biomarker for the risk of intestinal complications associated with COVID-19.(Figure Presented)RNA data from dataset GSE75214 demonstrating reduced ACE2 and increased CTSB and CTSL in patients with Crohn's disease during active inflammation compared to healthy controls. (Figure Presented) Enteroids from healthy control donors and patients with Crohn's disease were grown in 2D transwells and expression of indicated genes was assessed in pre-infection (A) and after infection with VSV-SARS-CoV-2 (B)

Acquisition of Furin Cleavage Site and Further SARS-CoV-2 Evolution Change the Mechanisms of Viral Entry, Infection Spread, and Cell Signaling.

Circulation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the human population leads to further viral evolution. The new variants that arise during this evolution are more infectious. Our data suggest that newer variants have shifted from utilizing both cathepsin/endosome- and TMPRSS2-mediated entry mechanisms to rely on a TMPRSS2-dependent entry pathway. Accordingly, only the early lineages of SARS-CoV-2 are capable of infecting and forming syncytia in Vero/ACE2 cells which lack TMPRSS2 expression. The presence of an intact multibasic furin cleavage site (FCS) in the S protein was a key requirement for cell-to-cell fusion. Deletion of FCS makes SARS-CoV-2 more infectious in vitro but renders it incapable of syncytium formation. Cell-to-cell fusion likely represents an alternative means of virus spread and is resistant to the presence of high levels of neutralizing monoclonal antibodies (MAbs) and immune sera in the media. In this study, we also noted that cells infected with SARS-CoV-2 with an intact FCS or alphavirus replicon expressing S protein (VEErep/S) released high levels of free S1 subunit. The released S1 is capable of activating the TLR4 receptor and inducing a pro-inflammatory response. Thus, S1 activation of TLR4 may be an important contributor to SARS-CoV-2-induced COVID-19 disease and needs to be considered in the design of COVID mRNA vaccines. Lastly, a VEErep/S-replicon was shown to produce large amounts of infectious, syncytium-forming pseudoviruses and thus could represent alternative experimental system for screening inhibitors of virus entry and syncytium formation. IMPORTANCE The results of this study demonstrate that the late lineages of SARS-CoV-2 evolved to more efficient use of the TMPRSS2-mediated entry pathway and gradually lost an ability to employ the cathepsins/endosome-mediated entry. The acquisition of a furin cleavage site (FCS) by SARS-CoV-2-specific S protein made the virus a potent producer of syncytia. Their formation is also determined by expression of ACE2 and TMPRSS2 and is resistant to neutralizing human MAbs and immune sera. Syncytium formation appears to be an alternative means of infection spread following the development of an adaptive immune response. Cells infected with SARS-CoV-2 with an intact FCS secrete high levels of the S1 subunit. The released S1 demonstrates an ability to activate the TLR4 receptor and induce pro-inflammatory cytokines, which represent a hallmark of SARS-CoV-2 pathogenesis. Alphavirus replicons encoding SARS-CoV-2 S protein cause spreading, syncytium-forming infection, and they can be applied as an experimental tool for studying the mechanism of syncytium formation.

Goblet Cell Hyperplasia Increases SARS-CoV-2 Infection in Chronic Obstructive Pulmonary Disease.

Chronic obstructive pulmonary disease (COPD) is one of the underlying conditions in adults of any age that place them at risk for developing severe illnesses associated with COVID-19. To determine whether SARS-CoV-2's cellular tropism plays a critical role in severe pathophysiology in the lung, we investigated its host cell entry receptor distribution in the bronchial airway epithelium of healthy adults and high-risk adults (those with COPD). We found that SARS-CoV-2 preferentially infects goblet cells in the bronchial airway epithelium, as mostly goblet cells harbor the entry receptor angiotensin-converting enzyme 2 (ACE2) and its cofactor transmembrane serine protease 2 (TMPRSS2). We also found that SARS-CoV-2 replication was substantially increased in the COPD bronchial airway epithelium, likely due to COPD-associated goblet cell hyperplasia. Likewise, SARS-CoV and Middle East respiratory syndrome (MERS-CoV) infection increased disease pathophysiology (e.g., syncytium formation) in the COPD bronchial airway epithelium. Our results reveal that goblet cells play a critical role in SARS-CoV-2-induced pathophysiology in the lung. IMPORTANCE SARS-CoV-2 or COVID-19's first case was discovered in December 2019 in Wuhan, China, and by March 2020 it was declared a pandemic by the WHO. It has been shown that various underlying conditions can increase the chance of having severe COVID-19. COPD, which is the third leading cause of death worldwide, is one of the conditions listed by the CDC which can increase the chance of severe COVID-19. The present study uses a healthy and COPD-derived bronchial airway epithelial model to study the COVID-19 and host factors which could explain the reason for COPD patients developing severe infection due to COVID-19.

Bronchial epithelia from adults and children: SARS-CoV-2 spread via syncytia formation and Type-III interferon infectivity restriction

Bronchi of the upper respiratory tract are considered the site of SARSCoV- 2 infection initiation from where a possible spread to the lower respiratory tract can cause acute respiratory distress syndrome with a high degree of mortality in elderly patients. Here we established functional reconstituted primary bronchial epithelia (BE) derived from donors including both adults and children to study SARS-CoV-2 infection dynamics in a physiologically relevant model. We identified multi-ciliated cells as the primary target cells for SARS-CoV-2 in our reconstituted BE. We further observed rapid viral spread throughout the entire BE within 24-48hours. Within 3-4 days, we observed syncytia formation between ciliated cells and basal cells which accumulate at the apical side of the BE. We show that infected cells including syncytia are released into the apical lumen and contribute to the transmittable virus dose. Interestingly, some BE mainly reconstituted from young donor, showed an intrinsic resistance to infection and virus spread. This restricted infection phenotype correlated with a faster release of type-III interferon secretion. Moreover, exogenous type-III interferon treatment to permissive epithelia installed infection restriction while interferon gene knockout promoted infection. Taken together our data uncover syncytia formation as possible contribution to tissue or environmental SARS-CoV-2 dissemination and the type-III IFN response as a central contributor to SARS-CoV-2 resistance in BE, which may explain epidemiological observations that SARS-CoV-2 fatality is age dependent.

Respiratory Syncytial and Parainfluenza Virus Infection Increase the Risk of Cytomegalovirus Reactivation in Allogeneic Hematopoietic Cell Transplant Recipients

Background. Respiratory virus infections are associated with significant and specific local and systemic inflammatory response patterns, which may lead to reactivation of latent viruses. We examined whether viral upper (URTI) or lower respiratory tract infection (LRTI) with common respiratory viruses increased the risk of CMV viremia after allogeneic hematopoietic cell transplantation (HCT). Methods. We retrospectively analyzed patients undergoing allogeneic HCT between 4/2008 and 9/2018. CMV surveillance was performed weekly and the presence of upper and lower respiratory symptoms were evaluated by multiplex respiratory viral PCR. We used Cox proportional hazards models to evaluate risk factors for development of any CMV viremia or high level CMV viremia in the first 100 days post-HCT. Each respiratory virus infection episode was considered positive for 30 days beginning the day of diagnosis. Results. Among 2,545 patients (404 children, 2141 adults), 1,221 and 247 developed CMV viremia and high level CMV viremia, respectively, in the first 100 days post-HCT. Infections due to human rhinoviruses (HRV, N=476) were most frequent, followed by parainfluenza viruses 1-4 (PIV, N=139), seasonal human coronaviruses (COV, N=134), respiratory syncytial virus (RSV, N=77), influenza A/B (FLU, N=35), human metapneumovirus (MPV, N=37), and adenovirus (ADV, N=61). In adjusted models, RSV LRTI was associated with increased risk of developing CMV viremia at all levels (Figures 1 and 2), and PIV or RSV URTI increased the risk of high level CMV viremia;all other viruses showed no association in univariable models. Figure 1. Model estimates for associations between LRTI and development of any CMV viremia Figure 2. Model estimates for associations between LRTI and development of high level CMV viremia Conclusion. We demonstrated that RSV and PIV infections are associated with an increased risk for development of CMV viremia after allogeneic HCT. This novel association provides the rationale to explore virus-specific inflammatory pathways that may trigger CMV reactivation. CMV viremia may also serve as an endpoint in clinical trials that assess new preventative or therapeutic interventions of RSV or PIV infection.

Cytoplasmic domain and enzymatic activity of ACE2 are not required for PI4KB dependent endocytosis entry of SARS-CoV-2 into host cells.

The recent COVID-19 pandemic poses a global health emergency. Cellular entry of the causative agent SARS-CoV-2 is mediated by its spike protein interacting with cellular receptor-human angiotensin converting enzyme 2 (ACE2). Here, by using lentivirus based pseudotypes bearing spike protein, we demonstrated that entry of SARS-CoV-2 into host cells was dependent on clathrin-mediated endocytosis, and phosphoinositides played essential roles during this process. In addition, we showed that the intracellular domain and the catalytic activity of ACE2 were not required for efficient virus entry. Finally, we showed that the current predominant Delta variant, although with high infectivity and high syncytium formation, also entered cells through clathrin-mediated endocytosis. These results provide new insights into SARS-CoV-2 cellular entry and present proof of principle that targeting viral entry could be an effective way to treat different variant infections.

Analysis of the Role of N-Linked Glycosylation in Cell Surface Expression, Function, and Binding Properties of SARS-CoV-2 Receptor ACE2.

Human angiotensin I-converting enzyme 2 (hACE2) is a type I transmembrane glycoprotein that serves as the major cell entry receptor for SARS-CoV and SARS-CoV-2. The viral spike (S) protein is required for the attachment to ACE2 and subsequent virus-host cell membrane fusion. Previous work has demonstrated the presence of N-linked glycans in ACE2. N-glycosylation is implicated in many biological activities, including protein folding, protein activity, and cell surface expression of biomolecules. However, the contribution of N-glycosylation to ACE2 function is poorly understood. Here, we examined the role of N-glycosylation in the activity and localization of two species with different susceptibility to SARS-CoV-2 infection, porcine ACE2 (pACE2) and hACE2. The elimination of N-glycosylation by tunicamycin (TM) treatment, or mutagenesis, showed that N-glycosylation is critical for the proper cell surface expression of ACE2 but not for its carboxiprotease activity. Furthermore, nonglycosylable ACE2 was localized predominantly in the endoplasmic reticulum (ER) and not at the cell surface. Our data also revealed that binding of SARS-CoV or SARS-CoV-2 S protein to porcine or human ACE2 was not affected by deglycosylation of ACE2 or S proteins, suggesting that N-glycosylation does not play a role in the interaction between SARS coronaviruses and the ACE2 receptor. Impairment of hACE2 N-glycosylation decreased cell-to-cell fusion mediated by SARS-CoV S protein but not that mediated by SARS-CoV-2 S protein. Finally, we found that hACE2 N-glycosylation is required for an efficient viral entry of SARS-CoV/SARS-CoV-2 S pseudotyped viruses, which may be the result of low cell surface expression of the deglycosylated ACE2 receptor. IMPORTANCE Understanding the role of glycosylation in the virus-receptor interaction is important for developing approaches that disrupt infection. In this study, we showed that deglycosylation of both ACE2 and S had a minimal effect on the spike-ACE2 interaction. In addition, we found that the removal of N-glycans of ACE2 impaired its ability to support an efficient transduction of SARS-CoV and SARS-CoV-2 S pseudotyped viruses. Our data suggest that the role of deglycosylation of ACE2 on reducing infection is likely due to a reduced expression of the viral receptor on the cell surface. These findings offer insight into the glycan structure and function of ACE2 and potentially suggest that future antiviral therapies against coronaviruses and other coronavirus-related illnesses involving inhibition of ACE2 recruitment to the cell membrane could be developed.

D614G Substitution of SARS-CoV-2 Spike Protein Increases Syncytium Formation and Virus Titer via Enhanced Furin-Mediated Spike Cleavage.

Since the D614G substitution in the spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged, the variant strain has undergone a rapid expansion to become the most abundant strain worldwide. Therefore, this substitution may provide an advantage for viral spreading. To explore the mechanism, we analyzed 18 viral isolates containing S proteins with either G614 or D614 (S-G614 and S-D614, respectively). The plaque assay showed a significantly higher virus titer in S-G614 than in S-D614 isolates. We further found increased cleavage of the S protein at the furin substrate site, a key event that promotes syncytium formation, in S-G614 isolates. The enhancement of the D614G substitution in the cleavage of the S protein and in syncytium formation has been validated in cells expressing S protein. The effect on the syncytium was abolished by furin inhibitor treatment and mutation of the furin cleavage site, suggesting its dependence on cleavage by furin. Our study pointed to the impact of the D614G substitution on syncytium formation through enhanced furin-mediated S cleavage, which might increase the transmissibility and infectivity of SARS-CoV-2 strains containing S-G614. IMPORTANCE Analysis of viral genomes and monitoring of the evolutionary trajectory of SARS-CoV-2 over time has identified the D614G substitution in spike (S) as the most prevalent expanding variant worldwide, which might confer a selective advantage in transmission. Several studies showed that the D614G variant replicates and transmits more efficiently than the wild-type virus, but the mechanism is unclear. By comparing 18 virus isolates containing S with either D614 or G614, we found significantly higher virus titers in association with higher furin protease-mediated cleavage of S, an event that promotes syncytium formation and virus infectivity, in the S-G614 viruses. The effect of the D614G substitution on furin-mediated S cleavage and the resulting enhancement of the syncytium phenotype has been validated in S-expressing cells. This study suggests a possible effect of the D614G substitution on S of SARS-CoV-2; the antiviral effect through targeting furin protease is worthy of being investigated in proper animal models.

Furin Inhibitors Block SARS-CoV-2 Spike Protein Cleavage to Suppress Virus Production and Cytopathic Effects.

Development of specific antiviral agents is an urgent unmet need for SARS-coronavirus 2 (SARS-CoV-2) infection. This study focuses on host proteases that proteolytically activate the SARS-CoV-2 spike protein, critical for its fusion after binding to angiotensin-converting enzyme 2 (ACE2), as antiviral targets. We first validate cleavage at a putative furin substrate motif at SARS-CoV-2 spikes by expressing it in VeroE6 cells and find prominent syncytium formation. Cleavage and the syncytium are abolished by treatment with the furin inhibitors decanoyl-RVKR-chloromethylketone (CMK) and naphthofluorescein, but not by the transmembrane protease serine 2 (TMPRSS2) inhibitor camostat. CMK and naphthofluorescein show antiviral effects on SARS-CoV-2-infected cells by decreasing virus production and cytopathic effects. Further analysis reveals that, similar to camostat, CMK blocks virus entry, but it further suppresses cleavage of spikes and the syncytium. Naphthofluorescein acts primarily by suppressing viral RNA transcription. Therefore, furin inhibitors may be promising antiviral agents for prevention and treatment of SARS-CoV-2 infection.

Methylation Pathways and SARS-CoV-2 Lung Infiltration and Cell Membrane-Virus Fusion Are Both Subject to Epigenetics.

The recent pandemic SARS-CoV-2 outbreak affects all kinds of individuals worldwide. The health, social, and economic impacts of the pandemic are dramatic, and vaccines or specific treatment options are not yet available. The only approaches that we currently have available to stop the epidemic are those of classical epidemic control, such as case isolation, contact tracing and quarantine, physical distancing, and hygiene measures. It is therefore essential to find further preventive measures and possible interventions that can slow down the number of infected individuals and decrease the severity of disease when affected by SARS-CoV-2. It seems that epigenetic mechanisms are an important part of the pathophysiology and illness severity of COVID-19. These mechanisms have been identified in SARS-CoV-2 but also in other viral infections. If and when these mechanisms are confirmed, then epigenetic interventions influencing DNA methylation could be indicated as primary and/or secondary preventive options.