AMYLOID FIBRILS INDUCE NEUTROPHIL EXTRACELLULAR TRAPS (NETS) IN THE LUNGS: IMPLICATIONS TO AMYLOID DISEASES

Amyloid fibrils (AF) are composed of misfolded proteins organized in a β-cross structure and are the hallmark of amyloid diseases such as Alzheimer's and Parkinson's. Neutrophil Extracellular Traps (NETs) are decondensed chromatin fibers decorated with antimicrobial proteins. Although NETs are important in immune homeostasis, they have been associated with tissue damage, autoimmunity, and metastasis, among others. Our group showed for the first time that, in vitro, human neutrophils incubated with AF release NETs in a NADPH oxidase (NOX-2)-dependent manner, and that neutrophil elastase presents in NETs digests AF forming cytotoxic oligomers. Now, we evaluated in vivo, through AF instillation into the lungs, whether AF induces NETs and how these NETs contribute to the progression of amyloid diseases. We used wildtype (WT) and NOX-2-deficient mice (KO). Our data showed that after 8h of instillation, α-synuclein AF were able to recruit leukocytes, especially neutrophils, in WT and KO animals, with more expressive recruitment in NOX-2-deficient mice. Photomicrographs of the BAL of both animals instilled with AF demonstrated the presence of neutrophils and mononuclear cells in a highly activated state only in KO animals. AF were visualized in the lungs of both animals, but disappeared over time in WT lungs, remaining intact in KO lungs, suggesting their fragmentation and/or phagocytosis. Immunofluorescence of the lungs of both animals revealed the presence of NETs only in WT animals, consistent with the inactivity of NOX-2 in KO mice. Oligomers derived from AF digestion were observed 24h after instillation in the lungs of WT mice, suggesting that proteases present in NETs may be responsible for AF degradation and oligomer formation as reported before in our in vitro studies. The persistence of AF compromised the function of the lungs of KO animals, but not the function of WT lungs, since after 8h, the AF disappeared from WT lungs due to NETs digestion. Our data suggest that instilled AF damage the lungs and induce NOX-2-dependent NET formation. As these AF are digested by the proteases present in NETs, lung function is recovered, and oligomers are formed. The fate and activity of these oligomers are under investigation in our lab.