The role of DNA Extracellular Traps (DETs) released by monocytes induced by SARS-CoV-2

It has been shown that SARS-CoV-2 induces the release of NETs, which are harmful to lung epithelial cells, were evidenced in lung biopsies, and correlated with COVID-19 severity. Similarly to NETs, monocytes release DNA Extracellular Traps (DETs) in response to various stimuli. Here, we evaluate whether SARS-CoV-2 and its spike protein induce the release of DETs in monocytes, determining the mechanisms involved in this process and investigating the possible pathogenic role of these DETs to cells. Our results confirm that human peripheral blood monocytes stimulated by beta-propriolactone-inactivated SARS-CoV-2 and its spike protein release DETs, measured by Picogreen assay. These DETs presented the characteristic morphology observed by scanning electron microscopy and immunofluorescence analysis with specific probes and antibodies showed the presence of DNA associated with elastase, myeloperoxidase (MPO), and citrullinated histone H3 in their composition. SARS-CoV-2 induces the production of reactive oxygen species in monocytes, the inhibition of which decreases DET extrusion. We used specific inhibitors to demonstrate that DET extrusion depends on MPO, peptidyl arginine deiminase, calcium, elastase, gasdermin-D, and NLRP3 inflammasome. Inhibition of TLR2, TLR4, and ACE2 receptors decreases DET release by monocytes. DETs were toxic to lung epithelial (A549 and Calu-3) and endothelial (hBMEC) cell lines as measured by resazurin reduction. DETs pretreated with anti-citrullinated histone antibody and elastase, as well as MPO inhibitors, decreased the toxicity to A549 cells, demonstrating the toxicity of these DET-associated molecules. The results indicate that SARS-CoV-2 induces the release of DETs in monocytes, which may participate in the pathophysiology of COVID-19. Procedures involving human cells were performed in accordance with the guidelines approved by the Ethics Committee for Human Studies of Hospital Clementino Fraga Filho (nº 4261015400005257).