Neutrophil Extracellular Traps Mediate In Vitro and In Vivo Degradation of α-Synuclein Amyloid Fibrils

Neutrophil extracellular traps (NETs) are chromatin-derived structures decorated with neutrophil enzymes such as elastase and myeloperoxidase. Our group has previously demonstrated that amyloid fibrils (AFs), regardless of their protein composition, induce NET release in vitro in human neutrophils through a process dependent on reactive oxygen species (ROS) generation by NADPH oxidase 2 (NOX-2). Moreover, the proteases embedded in NETs were shown to degrade AFs into smaller, potentially toxic species. The present study aimed to determine whether amyloid fibrils composed of α-synuclein (αSF) can induce NET formation in vivo and to investigate the role of NETs in modulating amyloid-associated pathology. To this end, we employed gp91phox knockout (KO) mice, which lack NOX-2 activity and are therefore unable to release NETs. αSF was instilled into the lungs of both WT and KO mice (males and females), leveraging the lung’s robust immune cell recruitment - particularly of neutrophils-as a model system. Eight hours after αSF instillation, both WT and KO animals exhibited marked neutrophil infiltration in the lungs causing inflammation. However, NET formation-evidenced by the presence of citrullinated histones and myeloperoxidase - was detected only in WT mice. Interestingly, while Congo red-positive amyloid-like structures persisted in the lungs of KO mice, they were absent in the lungs of WT animals, suggesting that NET-associated proteases facilitate the clearance of AFs from lung tissue. Lung function was assessed by measuring elastance and resistance. Our data showed that, while AFs were still present in the lungs of both WT and KO mice, elastance was impaired. As AFs were cleared from the lungs of WT mice, lung function recovered. In contrast, KO animals, in which AFs persisted, continued to exhibit compromised elastance. Together, our findings demonstrate that AFs impair lung function, and that NETs, induced in response to these fibrils, promote their degradation and thereby protect lung tissue from further damage.