Histones released by NETosis enhance the infectivity of SARS-CoV-2 by bridging the spike protein subunit 2 and sialic acid on host cells

Abstract

Neutrophil extracellular traps (NETs) can capture and kill viruses, such as influenza viruses, human immunodeficiency virus (HIV), and respiratory syncytial virus (RSV), thus contributing to host defense. Contrary to our expectation, we show here that the histones released by NETosis enhance the infectivity of SARS-CoV-2, as found by using live SARS-CoV-2 and two pseudovirus systems as well as a mouse model. The histone H3 or H4 selectively binds to subunit 2 of the spike (S) protein, as shown by a biochemical binding assay, surface plasmon resonance and binding energy calculation as well as the construction of a mutant S protein by replacing four acidic amino acids. Sialic acid on the host cell surface is the key molecule to which histones bridge subunit 2 of the S protein. Moreover, histones enhance cell–cell fusion. Finally, treatment with an inhibitor of NETosis, histone H3 or H4, or sialic acid notably affected the levels of sgRNA copies and the number of apoptotic cells in a mouse model. These findings suggest that SARS-CoV-2 could hijack histones from neutrophil NETosis to promote its host cell attachment and entry process and may be important in exploring pathogenesis and possible strategies to develop new effective therapies for COVID-19.

Molecular mechanisms and therapeutic target of NETosis in diseases

“…Furthermore, NETs can trap and eliminate pathogens to protect the host against viral infection. However, we found that histones, a major component of NETs, could enhance SARS‐CoV‐2 infection 142 . Mounting evidence shows that NETosis is associated with thrombosis, which is a significant predictor of disease severity in COVID‐19 patients 143 .…”

“…Moreover, cfDNA is linked to acute‐phase reactants and lactate dehydrogenase, as well as neutrophil count, while CitH3 is linked to platelet levels, supporting a function for NETosis in thrombosis 140 . Notably, SARS‐CoV‐2 can directly cause spontaneous NET release in vitro 141,142 …”

“…However, we found that histones, a major component of NETs, could enhance SARS‐CoV‐2 infection. 142 Mounting evidence shows that NETosis is associated with thrombosis, which is a significant predictor of disease severity in COVID‐19 patients. 143 In COVID‐19 patients, researchers discovered inflammatory microvascular thrombosis with NET‐associated fibrin and platelets in the heart, lung, and kidney; several neutrophil–platelet aggregates in the patients suffered from COVID‐19.…”

“…140 Notably, SARS-CoV-2 can directly cause spontaneous NET release in vitro. 141,142 Several studies have demonstrated a positive correlation between the presence of NETs and COVID-19 severity. Zuo et al 140 reported higher levels of cfDNA and MPO-DNA in patients treated with specific care and mechanical ventilation than in those breathing room air.…”

Therapy Targets SARS-CoV-2 Infection-Induced Cell Death

“…In addition to the NADPH oxidase (NOX)/ROS-, peptidylarginine deiminase 4 (PADI4)-, and NE-dependent pathways on the activation of NETosis, RIPK3/MLKL-mediated necroptosis and GSDMD-driven pyroptosis linked the excessive inflammatory response to NETosis ( 86 – 89 ). Emerging evidence from the clinic severe cases of COVID-19 implicated that NETosis and NET formation/release played a central role in the pathophysiology of inflammation, coagulopathy, immunothrombosis, and even organ damage during SARS-CoV-2 infection ( 90 – 94 ). With the growing roles of NETosis and NETs in COVID-19 reported, targeting dysregulated NETosis and NET formation/release is a new aspect of severe COVID-19 treatment.…”