Neutrophil-derived extracellular vesicles promote feed-forward inflammasome signaling in cystic fibrosis airways

Cystic fibrosis (CF) airways feature high extracellular levels of the IL-1 family of proinflammatory mediators. These mediators are cleavage products of caspase-1, the final protease in the inflammasome cascade. Due to the proven chronic presence of reprogrammed neutrophils in the CF airway lumen, understanding inflammasome signaling in these cells is of great importance to understand how disease is perpetuated in this milieu. Here, we hypothesized that CF airway neutrophils contribute to chronic inflammation, in part, via the packaging of inflammasome-inducing signals in extracellular vesicles (EVs). We confirmed that CF airway fluid is enriched in IL-1 alpha, IL-1 beta, and IL-18, and that CF airway neutrophils up-regulate the activating receptor IL-1R1. Meanwhile, down-modulatory signals such as IL-1R2 and IL-1RA are unchanged. Active caspase-1 itself is present in CF airway fluid EVs, with neutrophil-derived EVs being most enriched. Using a transmigration model of CF airway inflammation, we show that CF airway fluid EVs are necessary and sufficient to induce primary granule exocytosis by naive neutrophils (hallmark of reprogramming) and concomitantly activate caspase-1 and IL-1 beta production by these cells and that the addition of triple-combination highly effective CFTR modulator therapy does not abrogate these effects. Finally, EVs from activated neutrophils can deliver active caspase-1 to primary tracheal epithelial cells and induce their release of IL-1 alpha. These findings support the existence of a feed-forward inflammatory process by which reprogrammed CF airway neutrophils bypass 2-step control of inflammasome activation in neighboring cells (naive neutrophils and epithelial cells) via the transfer of bioactive EVs.

Automated summary

Neutrophils in cystic fibrosis (CF) airways contribute to chronic inflammation by packaging proinflammatory signals in extracellular vesicles (EVs). These EVs can induce reprogramming of naive neutrophils and activate caspase-1 and IL-1β production. Additionally, EVs from activated neutrophils can deliver active caspase-1 to tracheal epithelial cells and induce the release of IL-1α.