Activation of NLRP3 inflammasome by lymphocytic microparticles via TLR4 pathway contributes to airway inflammation

Abstract

The presence of elevated T lymphocytic microparticles (TLMPs) during respiratory illness is associated with airway and lung inflammation and epithelial injuries. Although inflammasome and IL-1β signaling are crucial in airway inflammation, little was known about their regulatory mechanism. We hypothesized that TLMPs trigger inflammasome activation and IL-1β production in bronchial and alveolar epithelial cells to induce airway and lung inflammation. In this study, TLMPs induced IL-1β and IL-18 secretion through NLRP3 inflammasome activation and upregulated TLR4 mRNA and protein expression in alveolar (A549) and human airway epithelial (16HBE) cells. Pretreatment with CLI-095, a specific inhibitor of TLR4 signaling, dramatically diminished the TLMP-induced release of IL-1β and IL-18 by inhibiting the formation of NLRP3/ASC/pro-caspase-1 inflammasome in a dose-dependent manner. The TLMP-induced autophagy inhibition in epithelial cells was dependent on the PI3K/Akt signaling pathway, which significantly increased NLRP3 expression and enhanced TLMP-induced inflammation. TLR4, IL-1β, and IL-18 proteins harbored in TLMPs were nonessential for the pro-inflammatory effect. In conclusion, TLMPs induce bronchial and alveolar epithelial cell secretion of IL-1β and IL-18 cytokines by activating the TLR4 and PI3K/Akt signaling pathways and inhibiting autophagy. These effects lead to NLRP3 inflammasome formation and accumulation. TLMPs may be regarded as deleterious markers of airway and lung damage in respiratory diseases.