Competitive cleavage of SARS-CoV-2 spike protein and epithelial sodium channel by plasmin as a potential mechanism for COVID-19 infection.

Cleavage of the furin site in SARS-CoV-2 spike (S) protein accounts for increased transmissibility of COVID-19 by promoting the entry of virus into host cells through specific angiotensin-converting enzyme 2 (ACE2) receptors. Plasmin, a key serine protease of fibrinolysis system, cleaves the furin site of γ subunit of human epithelial sodium channels (ENaCs). Sharing the plasmin cleavage by viral S and host ENaC proteins may competitively inter-regulate SARS-CoV-2 transmissibility and edema resolution via the ENaC pathway. To address this possibility, we analyzed single-cell RNA sequence (scRNA-seq) data sets and found that (encoding urokinase plasminogen activator), (γENaC), and (SARS-CoV-2 receptor) were co-expressed in airway/alveolar epithelial cells. The expression levels of and were significantly higher compared with in healthy group. This difference was further amplified in both epithelial and immune cells in patients with moderate/severe COVID-19 and SARS-CoV-2 infected airway/alveolar epithelial cell lines. Of note, plasmin cleaved the S protein and facilitated the entry of pseudovirus in HEK293 cells. Conclusively, SARS-CoV-2 may expedite infusion by competing the fibrinolytic protease network with ENaC.