Identifizierung eines feedback-loop Mechanismus zwischen Neutrophilen und Makrophagen zur Aufrechterhaltung einer Metastasen-fördernden Inflammation
Hämatologie, Onkologie
Zusammenfassung der Projektergebnisse
Cell-cell communication maintains biological functions and homeostasis of cells and organs but is dysregulated in many inflammatory pathologies. The communication between cells can occur by different means, and nucleic acids released from dying cells is one example of active information exchange to living cells. The specialized cell death pathway in neutrophils called NETosis induces the release of neutrophil extracellular traps (NETs) – structures generated by the expulsion of the neutrophil’s nucleic acids with associated proteins. NETs can capture and kill pathogens but excessive NET release occurs in several inflammatory pathologies, including sepsis. Moreover, the appearance of NETs has also been described in different IL-1b driven inflammatory diseases, e.g. sepsis, but the link between NETs and IL-1b remains elusive. Increased IL-1b levels are caused by inflammasome activation. Inflammasomes are key sensors in innate immunity, capable of detecting pathogens and dangerassociated molecular patterns. They are large multi-protein complexes and their activation leads to the activation of caspase-1, which in turn generates mature IL-1b. To evaluate the contribution of NETs in the establishment of an inflammatory response through inflammasome activation, human neutrophils or human neutrophil-like cells (HL60) were induced to form NETs. NETs triggered the release of inflammatory cytokines IL-1b, and TNFa but not CXCL10 and IL-6 in monocytic cells. Interestingly, the release of IL-1b was independent of NET DNA, suggesting that specific components on the NETs and not simply the DNA triggered the activation. To assess the signaling pathway responsible for inflammasome activation by NETs, we used CRISPR/cas9-engineered knock THP1 cells, and determined that NETs activate the NLRP3 inflammasome subtype. The NLRP3 inflammasome is activate by divers stimuli, including ionic influx, reactive oxygen species and RNA:DNA hybrids. Digestion of NETs with RNase H or treatment of NETs with an RNA:DNA hybrid specific blocking antibody abolished NET-induced IL-1b secretion indicating the presence of RNA:DNA hybrids within NETs. Furthermore, induction of acute sepsis in mice triggered the formation of NETs associated with RNA:DNA hybrids in vivo. In conclusion, the presence of RNA:DNA hybrids highlights a so far undiscovered molecular messenger within NETs responsible for the secretion of IL-1b in monocytes by activating the NLRP3 inflammasome. Understanding the mechanisms of NET sensing by the immune system will help us to evaluate the impact of NETs in inflammatory diseases and further evaluation of specific NET structures will help to determine therapeutic targets in NET-associated diseases.
