Fibrinolysis influences SARS-CoV-2 infection in ciliated cells.

Rapid spread of COVID-19 has caused an unprecedented pandemic worldwide, and an inserted furin site in SARS-CoV-2 spike protein (S) may account for increased transmissibility. Plasmin, and other host proteases, may cleave the furin site of SARS-CoV-2 S protein and γ subunits of epithelial sodium channels (γ ENaC), resulting in an increment in virus infectivity and channel activity. As for the importance of ENaC in the regulation of airway surface and alveolar fluid homeostasis, whether SARS-CoV-2 will share and strengthen the cleavage network with ENaC proteins at the single-cell level is urgently worthy of consideration. To address this issue, we analyzed single-cell RNA sequence (scRNA-seq) datasets, and found the PLAU (encoding urokinase plasminogen activator), SCNN1G (γENaC), and ACE2 (SARS-CoV-2 receptor) were co-expressed in alveolar epithelial, basal, club, and ciliated epithelial cells. The relative expression level of PLAU, TMPRSS2, and ACE2 were significantly upregulated in severe COVID-19 patients and SARS-CoV-2 infected cell lines using Seurat and DESeq2 R packages. Moreover, the increments in PLAU, FURIN, TMPRSS2, and ACE2 were predominately observed in different epithelial cells and leukocytes. Accordingly, SARS-CoV-2 may share and strengthen the ENaC fibrinolytic proteases network in ACE2 positive airway and alveolar epithelial cells, which may expedite virus infusion into the susceptible cells and bring about ENaC associated edematous respiratory condition.