ABSTRACT
The novel severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) caused the devastating ongoing coronavirus disease-2019 (COVID-19) pandemic which poses a great threat to global public health. The spike (S) polypeptide of SARS-CoV-2 consists of the S1 and S2 subunits and is processed by cellular proteases at the S1/S2 boundary. The inclusion of the 4 amino acids (PRRA) at the S1/S2 boundary forms a furin cleavage site (FCS), 682RRAR{downarrow}S686, distinguishing SARS-CoV-2 from its closest relative, the SARS-CoV. Various deletions surrounding the FCS have been identified in patients. When SARS-CoV-2 propagated in Vero cells, the virus acquired various deletions surrounding the FCS. In the present study, we studied the viral transcriptome in SARS-CoV-2 infected primary human airway epithelia (HAE) cultured at an air-liquid interface (ALI) with an emphasis on the viral genome stability at the S1/S2 boundary using RNA-seq. 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 S1/S2 boundary of the S gene: one is a deletion of 12 amino acids, 678TNSPRRAR{downarrow}SVAS689, which contains the FCS, another is a deletion of 5 amino acids, 675QTQTN679, which is two amino acids upstream of the FCS. Further studies on the dynamics of the FCS deletions in apically released virions revealed that the selective pressure for the FCS maintains the S gene stability in HAE-ALI but with exceptions, in which the FCS deletions are remained at a high rate. Thus, 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 donor-dependent.
ABSTRACT
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replicates throughout human airways. The polarized human airway epithelium (HAE) cultured at an airway-liquid interface (HAE-ALI) is an in vitro model mimicking the in vivo human mucociliary airway epithelium and supports the replication of SARS-CoV-2. However, previous studies only characterized short-period SARS-CoV-2 infection in HAE. In this study, continuously monitoring the SARS-CoV-2 infection in HAE-ALI cultures for a long period of up to 51 days revealed that SARS-CoV-2 infection was long lasting with recurrent replication peaks appearing between an interval of approximately 7-10 days, which was consistent in all the tested HAE-ALI cultures derived from 4 lung bronchi of independent donors. We also identified that SARS-CoV-2 does not infect HAE from the basolateral side, and the dominant SARS-CoV-2 permissive epithelial cells are ciliated cells and goblet cells, whereas virus replication in basal cells and club cells was not detectable. Notably, virus infection immediately damaged the HAE, which is demonstrated by dispersed Zonula occludens-1 (ZO-1) expression without clear tight junctions and partial loss of cilia. Importantly, we identified that SARS-CoV-2 productive infection of HAE requires a high viral load of 2.5 x 105 virions per cm2 of epithelium. Thus, our studies highlight the importance of a high viral load and that epithelial renewal initiates and maintains a recurrent infection of HAE with SARS-CoV-2.
ABSTRACT
Objective To investigate whether ROS/JNK/Egr-1 signaling pathway was activated in cardiomyocytes after hypoxia/reoxygenation ( H/R).Methods H9c2 cardiomyocytes were grouped randomly as follows: control group, H/R group, control +the ROS donor xanthine oxidase /hypoxanthine (XO/HX) group, H/R +the ROS scavenger edaravones (EDA) group, H/R +the ROS scavenger N-acetyl-L-cysteine (NAC) group, H/R +JNK inhibitor SP60012 group.To establish H9c2 H/R models and the myocardial cells were treated with different concentrations of EDA (2 × 10 -6,2 ×10 -5,2 ×10 -4 M), NAC (5 ×10 -4,2 ×10 -3,8 ×10 -3 M), XO/HX (1mU/mL/1.2 ×10 -4 M , 3mU/mL/3.6 ×10 -4 M, 5mU/mL/6.0 × 10 -4 M) and SP600125 (2 ×10 -5 M).ROS level was measured by flow cytometry, and Egr-1, p-JNK and total JNK protein levels were detected by Western blot.ResuIts ROS levels and Egr-1 protein levels in H/R group were significantly higher than control group (P<0.05).The moderate and high concentrations EDA and NAC of ROS scavenger significantly decreased the high levels of ROS and Egr-1 protein ( P<0.05 ) , but there were no significant differences of low concentration.There was a significant positive correlation between ROS levels and Egr-1 protein (r=0.91,P<0.01).JNK activation levels in each concentrations of XO/HX were significantly higher than control group, and JNK activation increased with the increasing of XO/HX concentrations (P<0.05).JNK activation level in H/R group was higher than control group, after treated by EDA and NAC of ROS scavenger and JNK inhibitor, JNA activation reduced (P<0.05).Egr-1 protein levels in H/R group was higher than that in control group, and JNK inhibitor reduced the expression of Egr-1 protein induced by H/R.ConcIusion H/R activates ROS/Egr-1 signaling pathway in H9c2 cardiomyocytes, and JNK activation plays an important role in this pathway.
