NET amyloidogenic backbone in human activated neutrophils

Abstract

SummaryActivated human neutrophils produce a fibrillar DNA network [neutrophil extracellular traps (NETs)] for entrapping and killing bacteria, fungi, protozoa and viruses. Our results suggest that the neutrophil extracellular traps show a resistant amyloidogenic backbone utilized for addressing reputed proteins and DNA against the non-self. The formation of amyloid fibrils in neutrophils is regulated by the imbalance of reactive oxygen species (ROS) in the cytoplasm. The intensity and source of the ROS signal is determinant for promoting stress-associated responses such as amyloidogenesis and closely related events: autophagy, exosome release, activation of the adrenocorticotrophin hormone/ a-melanocyte-stimulating hormone (ACTH/a-MSH) loop and synthesis of specific cytokines. These interconnected responses in human activated neutrophils, that have been evaluated from a morphofunctional and quantitative viewpoint, represent primitive, but potent, innate defence mechanisms. In invertebrates, circulating phagocytic immune cells, when activated, show responses similar to those described previously for activated human neutrophils. Invertebrate cells within endoplasmic reticulum cisternae produce a fibrillar material which is then assembled into an amyloidogenic scaffold utilized to convey melanin close to the invader. These findings, in consideration to the critical role played by NET in the development of several pathologies, could explain the structural resistance of these scaffolds and could provide the basis for developing new diagnostic and therapeutic approaches in immunomediated diseases in which the innate branch of the immune system has a pivotal role.

Conservative Mechanisms of Extracellular Trap Formation by Annelida Eisenia andrei: Serine Protease Activity Requirement

“…Importantly, amyloid fibrils also accumulate in mammals, thus are evolutionary conserved [ 74 ], but their deposition mostly leads to pathological diseases such as Alzheimer disease [ 78 , 79 ]. Interestingly, amyloid fibrils can induce formation of ETs by neutrophils [ 80 ] but they also attach to neutrophil ETs where they address raptured proteins and DNA against the non-self [ 80 ].…”

MCF7 Spheroid Development: New Insight about Spatio/Temporal Arrangements of TNTs, Amyloid Fibrils, Cell Connections, and Cellular Bridges

“…Amyloid fibril characterization: amyloid structures were identified according to Le Vine III [ 80 ] by staining with ThS and visualizing the amyloid-specific green/yellow fluorescence with a Leica laser confocal microscope. Amyloid fibrils were also localized immunocytochemically, using an antibody directed against Pmel17, which is one of the proteins able to form amyloid fibrillar structures in mammals [ 26 , 54 , 81 , 82 ] ( Table 1 ).…”

Alzheimer’s Amyloid-β is an Antimicrobial Peptide: A Review of the Evidence

“…Amyloid structures that could be stained with Congo red and thioflavin-s were observed in activated neutrophils, and were found to colocalize with the DNA of the extracellular NET structures. The positive charge of the NET amyloid likely assists in targeting microbes, allowing it to distinguish between negatively-charged pathogen membranes and zwitterionic host membranes [65]. In addition to neutrophils, activated eosinophils, monocytes/macrophages and mast cells can secrete NETs, suggesting that amyloid bioflocculants could be an integral part of human innate immunity [66][67][68].…”