Activation of NLRP3 inflammasome in alveolar macrophages contributes to mechanical stretch-induced lung inflammation and injury.

Mechanical ventilation of lungs is capable of activating the innate immune system and inducing sterile inflammatory response. The proinflammatory cytokine IL-1β is among the definitive markers for accurately identifying ventilator-induced lung inflammation. However, mechanisms of IL-1β release during mechanical ventilation are unknown. In this study, we show that cyclic stretch activates the nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3) inflammasomes and induces the release of IL-1β in mouse alveolar macrophages via caspase-1- and TLR4-dependent mechanisms. We also observed that NADPH oxidase subunit gp91(phox) was dispensable for stretch-induced cytokine production, whereas mitochondrial generation of reactive oxygen species was required for stretch-induced NLRP3 inflammasome activation and IL-1β release. Further, mechanical ventilation activated the NLRP3 inflammasomes in mouse alveolar macrophages and increased the production of IL-1β in vivo. IL-1β neutralization significantly reduced mechanical ventilation-induced inflammatory lung injury. These findings suggest that the alveolar macrophage NLRP3 inflammasome may sense lung alveolar stretch to induce the release of IL-1β and hence may contribute to the mechanism of lung inflammatory injury during mechanical ventilation.