Neutrophil extracellular traps contain mitochondrial as well as nuclear DNA and exhibit inflammatory potential

Abstract

Neutrophils expel extracellular traps (NETs) to entrap and exterminate the invaded microorganisms. Acute/chronic inflammatory disorders are often observed with aberrantly enhanced NETs formation and high nitric oxide (NO) availability. Recent study from this lab demonstrated release of NETs from human neutrophils following treatment with SNP or SNAP. The present study is an extension of our previous finding to explore the extracellular bacterial killing, source of DNA in the expelled NETs, their ability to induce pro-inflammatory cytokines release from platelets/THP-1 cells and assessment of NO mediated free radical formation by using a consistent NO donor, DETA-NONOate. NO mediated NETs exhibited extracellular bacterial killing as determined by colony forming units. NO mediated NETs formation was due to the activation of NADPH oxidase and myeloperoxidase. NO or PMA mediated NETs were positive for both nuclear and mitochondrial DNA as well as proteolytic enzymes. Incubation of NETs with human platelets enhanced the release of IL-1β and IL-8, while with THP-1 cells release of IL-1β, IL-8 and TNFα was observed. The present study demonstrates that NO by augmenting enzymatic free radical generation release NETs to promote extracellular bacterial killing. These NETs were made up of mitochondrial and nuclear DNA and potentiated release of pro-inflammatory cytokines.