Signal transduction regulating formation of neutrophil extracellular traps (NETs) in response to the yeast surface component beta-glucan: role of Src-family kinases and Syk

Upon activation, neutrophils release extracellular fibers or neutrophil extracellular traps (NETs), structures composed of chromatin and granule proteins that bind and kill pathogens. However, NETs can contribute to systemic and local pathologies such as sepsis, vasculitis and chronic lung pathologies like cystic fibrosis. Signal transduction mechanisms regulating NET formation are poorly understood. In fact, the only pathway identified so far to be able to induce NET formation is one based on a protein kinase C/reactive oxygen intermediates (ROIs) module. Given the important role of Src kinase family (SFKs) in inflammatory pathologies, we addressed whether SFKs and Syk, a cytoplasmic tyrosine kinase placed downstream SFK-regulated signal transduction pathways in leukocytes regulate NET formation. To this purpose, NETs were examined in human and murine neutrophils stimulated with different agonists, including beta-glucan (BG), a yeast surface component recognized by the C-type lectin receptor Dectin-1. The SFKs inhibitor PP2 and the Syk inhibitor PRT-060318 were used as selective drugs targeting the Dectin-1 triggered signaling pathway. Here we show that beta-glucan is an effective stimulus for the induction of NETs, displaying its effects even earlier than PMA. Additionally, in this work we demonstrate that beta-glucan-induced NETs requires both SFKs and ROS production though we did not identified the SFK involved. Differently from BG, PMA induced NET release in a manner dependent on ROS production but not on SFKs. Our data highlight also the role of Syk in NET formation triggered by beta-glucan. In conclusion, in this project we identified some possible drug targets to modulate NET formation and to avoid the pathogenic side of NETs.