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The role of selected mitochondrial proteins in neutrophil extracellular DNA trap formation

  • Fartelj, David
Publication Date
Sep 18, 2020
University of Ljubljana
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Neutrophils represent the majority of all immune cells and are arguably the most important cells of the innate immune system. Their response may be non-specific, but they are one of the first recognition sites against invading microorganisms. They can ingest a variety of pathogens by phagocytosis, destroying them in intracellular vesicles containing degrading enzymes and other antimicrobial substances. Besides to that, neutrophils possess a recently discovered mechanism to kill microbes extracellularly. During an infection, neutrophils release a structure with a DNA scaffold containing granule proteins called neutrophil extracellular traps (NETs). These structures are able to bind and kill pathogens. It is known that viable neutrophils can form NETs made up of mitochondrial DNA and granule proteins after short stimulation with GM-CSF and C5a. The goal of the thesis was to investigate the mechanism of NET formation using genetic and pharmacological approaches. We used genetically modified Hoxb8 mouse neutrophils and human neutrophils to study the molecular mechanisms of dsDNA release and NET formation. For the evaluation of the NETs, we used confocal laser scanning microscopy and PicoGreen dsDNA quantitation assay to quantify the released dsDNA in culture supernatants. Using Hoxb8 mouse and freshly isolated human neutrophils, we evaluated the importance of the pro-apoptotic proteins BAX and BAK, as well as the voltage-dependent anion-selective channel 1 (VDAC1) and Gasdermin D (GSDMD) for ROS production and NET formation. We demonstrate that both BAX and BAK may play a role in NET formation in the absence of cell death. We demonstrated that mouse neutrophils deficient in BAX or BAK exhibit reduced NET formation upon activation. In addition, using an inhibitor of voltage-dependent anion-selective channel 1 (VDAC1) oligomerization, we could determine that the formation of NETs does not require mitochondrial permeability transition pore (MPTP). Lastly, our results showed that GSDMD-dependent pyroptotic cell death does not play any role in mouse or human neutrophils NET formation.

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