Amoeba use DNA based Neutrophil Extracellular Traps (DNA NETS) to expel the threats of bacteria and other pathogens that might threaten their existence. Neutrophil extracellular traps (NETs) is a naturally occurring biotechnology phenomenon that is used by most organisms to enhance their immunologic response to pathogens (Sørensen, & Borregaard, 2016). NETs were first described in 2004. Studies show that the NETs are composed of filamentous diffused chromatin-histone structures fused with lytic and bactericidal proteins such as myeloperoxidase and neutrophil elastase (Sørensen, & Borregaard, 2016). Chromatin decondensation and spreading result in the release of the net DNA structures. Nucleus material i.e. histones and chromatin have intrinsic antimicrobial activity. The exact molecular pathways involved in the molecular pathway of the DNA NETS formation still remain unclear. However, some studies indicate that DNA decondensation is the primary mechanism. Most of the DNA of neutrophils is transcriptionally inactive. The organization of the DNA in the cellular nucleus involves condensation into heterochromatin structures. The basic DNA structure in the nucleus are wrapped around histone proteins. These are then organized to form the DNA nucleosomes which are then packaged into chromatins. The histone-DNA binding is potentiated by the strong positive charge on the arginine residues (Sørensen, & Borregaard, 2016). According to Díaz-Godínez et al., (2018) increased cellular calcium results in the generation of reactive oxygen species (ROS) by NADPH oxidase is one of the trigger mechanisms that causes the decondensation of the nuclear DNA material. Both nuclear and mitochondrial DNA (mtDNA) have been implicated in the formation of the NETs.
Díaz-Godínez et al., (2018) point out that neutrophil elastase (NE) plays an important role in the formation of phagocytic NET structures. Generation of reactive oxygen species as a result of extracellular calcium influx enhances the movement of NE from the cytoplasmic cellular compartment to the nuclear material. Neutrophil elastase then potentiates the cleaving of the histone proteins hence initiating the decondensation of DNA. Introducing peptidyl arginine deiminase 4 (PAD4) into the cell may also cause the decondensation of the DNA independently without the involvement of NADPH oxidase derived ROS. This mechanism also involves calcium ionospheres ionomycin, and occur by the neutralization of positively charged arginine residues on the histone proteins (Díaz-Godínez et al., 2018). According to Sørensen, & Borregaard, (2016) the resulting uncharged citrulline residues weaken the histone-DNA binding, making it possible to unwarp the nucleosome structures.
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Early studies described the mechanism involved in the biotechnological phenomenon as suicidal NETosis. In this mechanism, the cells were said to dismantle their intracellular structures and spill their contents including DNA, bactericidal proteins, and chromatin to the outside of the cell in a big fish net manner. These DNA containing materials were responsible for fighting the foreign organisms. However, this mechanism is said to be harmful to the cell, as it kills both the host’s immune cells and the microbes (Sørensen, & Borregaard, 2016). NETosis might artificially be triggered by using chemicals such as phorbol myristate acetate (PMA) which cause a rapid burst of the cells. PMA manipulates the cellular content and the nuclear material, causing the DNA to unfold and significantly increase in size. The intracellular membranes eventually dissolve potentially resulting in the death of the cell and release of their contents. Besides microbes and pathogens, NETosis might also occur under sterile conditions, resulting in autoimmune conditions. NETosis does not always result in the death of the cell. Some cells develop a biotechnological mechanism of remaining alive even after tossing out all their nuclear contents (Sørensen, & Borregaard, 2016). This mechanism is described as vital NETosis.
Induction and investigation of NET formation is easier in vitro than in vivo as it is easy to control the studies. Blood samples are utilized in in vitro studies, from which neutrophils are isolated. In in vivo studies, activated endothelium technique is used to capture neutrophils which are then directed to the site of infection (Sørensen, & Borregaard, 2016). As mentioned earlier, PMA is the preferred agent for inducing and investigating NET formation in vitro . Myeloperoxidase catalyzed (MPO) the activity of PMA. NETosis may be interfered with by the inhibition of MPO activity.
References
Díaz-Godínez, C., Fonseca, Z., Néquiz, M., Laclette, J. P., Rosales, C., & Carrero, J. C. (2018). Entamoeba histolytica Trophozoites Induce a Rapid Non-classical NETosis Mechanism Independent of NOX2-Derived Reactive Oxygen Species and PAD4 Activity. Frontiers in cellular and infection microbiology , 8 , 184. doi:10.3389/fcimb.2018.00184
Sørensen, O. E., & Borregaard, N. (2016). Neutrophil extracellular traps—the dark side of neutrophils. The Journal of clinical investigation , 126 (5), 1612-1620.
