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The SARS-CoV-2 Transcriptome and the Dynamics of the S Gene Furin Cleavage Site in Primary Human Airway Epithelia.

ABSTRACT: The spike (S) polypeptide of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) consists of the S1 and S2 subunits and is processed by cellular proteases at the S1/S2 boundary that contains a furin cleavage site (FCS), ⁶⁸²RRAR↓S⁶⁸⁶ Various deletions surrounding the FCS have been identified in patients. When SARS-CoV-2 propagated in Vero cells, it acquired deletions surrounding the FCS. We studied the viral transcriptome in Vero cell-derived SARS-CoV-2-infected primary human airway epithelia (HAE) cultured at an air-liquid interface (ALI) with an emphasis on the viral genome stability of the FCS. While we found overall the viral transcriptome is similar to that generated from infected Vero cells, we identified a high percentage of mutated viral genome and transcripts in HAE-ALI. Two highly frequent deletions were found at the FCS region: a 12 amino acid deletion (⁶⁷⁸TNSPRRAR↓SVAS⁶⁸⁹) that contains the underlined FCS and a 5 amino acid deletion (⁶⁷⁵QTQTN⁶⁷⁹) that is two amino acids upstream of the FCS. Further studies on the dynamics of the FCS deletions in apically released virions from 11 infected HAE-ALI cultures of both healthy and lung disease donors revealed that the selective pressure for the FCS maintains the FCS stably in 9 HAE-ALI cultures but with 2 exceptions, in which the FCS deletions are retained at a high rate of >40% after infection of ≥13 days. Our study presents evidence for the role of unique properties of human airway epithelia in the dynamics of the FCS region during infection of human airways, which is likely donor dependent.IMPORTANCE Polarized human airway epithelia at an air-liquid interface (HAE-ALI) are an in vitro model that supports efficient infection of SARS-CoV-2. The spike (S) protein of SARS-CoV-2 contains a furin cleavage site (FCS) at the boundary of the S1 and S2 domains which distinguishes it from SARS-CoV. However, FCS deletion mutants have been identified in patients and in vitro cell cultures, and how the airway epithelial cells maintain the unique FCS remains unknown. We found that HAE-ALI cultures were capable of suppressing two prevalent FCS deletion mutants (Δ⁶⁷⁸TNSPRRAR↓SVAS⁶⁸⁹ and Δ⁶⁷⁵QTQTN⁶⁷⁹) that were selected during propagation in Vero cells. While such suppression was observed in 9 out of 11 of the tested HAE-ALI cultures derived from independent donors, 2 exceptions that retained a high rate of FCS deletions were also found. Our results present evidence of the donor-dependent properties of human airway epithelia in the evolution of the FCS during infection.

SUBMITTER: Zou W

PROVIDER: S-EPMC8262919 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:SARS-CoV-2 has resulted in a global pandemic and shutdown economies around the world. Sequence analysis indicates that the novel coronavirus (CoV) has an insertion of a furin cleavage site (PRRAR) in its spike protein. Absent in other group 2B CoVs, the insertion may be a key factor in the replication and virulence of SARS-CoV-2. To explore this question, we generated a SARS-CoV-2 mutant lacking the furin cleavage site (?PRRA) in the spike protein. This mutant virus replicated with faster kinetics and improved fitness in Vero E6 cells. The mutant virus also had reduced spike protein processing as compared to wild-type SARS-CoV-2. In contrast, the ?PRRA had reduced replication in Calu3 cells, a human respiratory cell line, and had attenuated disease in a hamster pathogenesis model. Despite the reduced disease, the ?PRRA mutant offered robust protection from SARS-CoV-2 rechallenge. Importantly, plaque reduction neutralization tests (PRNT 50 ) with COVID-19 patient sera and monoclonal antibodies against the receptor-binding domain found a shift, with the mutant virus resulting in consistently reduced PRNT 50 titers. Together, these results demonstrate a critical role for the furin cleavage site insertion in SARS-CoV-2 replication and pathogenesis. In addition, these findings illustrate the importance of this insertion in evaluating neutralization and other downstream SARS-CoV-2 assays. Importance:As COVID-19 has impacted the world, understanding how SARS-CoV-2 replicates and causes virulence offers potential pathways to disrupt its disease. By removing the furin cleavage site, we demonstrate the importance of this insertion to SARS-CoV-2 replication and pathogenesis. In addition, the findings with Vero cells indicate the likelihood of cell culture adaptations in virus stocks that can influence reagent generation and interpretation of a wide range of data including neutralization and drug efficacy. Overall, our work highlights the importance of this key motif in SARS-CoV-2 infection and pathogenesis. Article Summary:A deletion of the furin cleavage site in SARS-CoV-2 amplifies replication in Vero cells, but attenuates replication in respiratory cells and pathogenesis in vivo. Loss of the furin site also reduces susceptibility to neutralization in vitro .

Project description:BackgroundThe coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a worldwide pandemic with over 627 million cases and over 6.5 million deaths. It was reported that smoking-related chronic obstructive pulmonary disease (COPD) might be a crucial risk for COVID-19 patients to develop severe condition. As cigarette smoke (CS) is the major risk factor for COPD, we hypothesize that barrier dysfunction and an altered cytokine response in CS-exposed airway epithelial cells may contribute to increased SARS-CoV-2-induced immune response that may result in increased susceptibility to severe disease. The aim of this study was to evaluate the role of CS on SARS-CoV-2-induced immune and inflammatory responses, and epithelial barrier integrity leading to airway epithelial damage.MethodsPrimary human airway epithelial cells were differentiated under air-liquid interface culture. Cells were then exposed to cigarette smoke medium (CSM) before infection with SARS-CoV-2 isolated from a local patient. The infection susceptibility, morphology, and the expression of genes related to host immune response, airway inflammation and damages were evaluated.ResultsCells pre-treated with CSM significantly caused higher replication of SARS-CoV-2 and more severe SARS-CoV-2-induced cellular morphological alteration. CSM exposure caused significant upregulation of long form angiotensin converting enzyme (ACE)2, a functional receptor for SARS-CoV-2 viral entry, transmembrane serine protease (TMPRSS)2 and TMPRSS4, which cleave the spike protein of SARS-CoV-2 to allow viral entry, leading to an aggravated immune response via inhibition of type I interferon pathway. In addition, CSM worsened SARS-CoV-2-induced airway epithelial cell damage, resulting in severe motile ciliary disorder, junctional disruption and mucus hypersecretion.ConclusionSmoking led to dysregulation of host immune response and cell damage as seen in SARS-CoV-2-infected primary human airway epithelia. These findings may contribute to increased disease susceptibility with severe condition and provide a better understanding of the pathogenesis of SARS-CoV-2 infection in smokers.

Project description:SARS-CoV-2 infection causing the COVID-19 pandemic calls for immediate interventions to avoid viral transmission, disease progression, and subsequent excessive inflammation and tissue destruction. Primary normal human bronchial epithelial cells are among the first targets of SARS-CoV-2 infection. Here, we show that ColdZyme medical device mouth spray efficiently protected against virus entry, excessive inflammation, and tissue damage. Applying ColdZyme to fully differentiated, polarized human epithelium cultured at an air-liquid interphase (ALI) completely blocked binding of SARS-CoV-2 and increased local complement activation mediated by the virus as well as productive infection of the tissue model. While SARS-CoV-2 infection resulted in exaggerated intracellular complement activation immediately following infection and a drop in transepithelial resistance, these parameters were bypassed by single pretreatment of the tissues with ColdZyme mouth spray. Crucially, our study highlights the importance of testing already evaluated and safe drugs such as ColdZyme mouth spray for maintaining epithelial integrity and hindering SARS-CoV-2 entry within standardized three-dimensional (3D) in vitro models mimicking the in vivo human airway epithelium.IMPORTANCE Although our understanding of COVID-19 continuously progresses, essential questions regarding prophylaxis and treatment remain open. A hallmark of severe SARS-CoV-2 infection is a hitherto-undescribed mechanism leading to excessive inflammation and tissue destruction associated with enhanced pathogenicity and mortality. To tackle the problem at the source, transfer of SARS-CoV-2, subsequent binding, infection, and inflammatory responses have to be avoided. In this study, we used fully differentiated, mucus-producing, and ciliated human airway epithelial cultures to test the efficacy of ColdZyme medical device mouth spray in terms of protection from SARS-CoV-2 infection. Importantly, we found that pretreatment of the in vitro airway cultures using ColdZyme mouth spray resulted in significantly shielding the epithelial integrity, hindering virus binding and infection, and blocking excessive intrinsic complement activation within the airway cultures. Our in vitro data suggest that ColdZyme mouth spray may have an impact in prevention of COVID-19.

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The SARS-CoV-2 Transcriptome and the Dynamics of the S Gene Furin Cleavage Site in Primary Human Airway Epithelia.

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