Platelet Extracellular Vesicles Drive Inflammasome-IL1β-dependent Lung Injury in Sickle Cell Disease.

RATIONALE: Intra-erythrocytic polymerization of hemoglobin S promotes hemolysis and vaso-occlusive events in the microvasculature of sickle cell disease (SCD) patients. Although platelet-neutrophil aggregates-dependent vaso-occlusion is known to occur in the lung and contribute to acute chest syndrome, the etiological mechanisms that trigger lung injury are largely unknown.

OBJECTIVES: To identify the innate-immune mechanism that promotes platelet-neutrophil aggregate-dependent lung vaso-occlusion and injury in SCD.

METHODS: In vivo imaging of the lung in transgenic humanized SCD mice and in vitro imaging of SCD patient blood flowing through a microfluidic system was performed. SCD mice were systemically challenged with nanogram quantities of lipopolysaccharide to trigger lung vaso-occlusion.

MAIN RESULTS: Platelet-inflammasome activation led to generation of IL-1β carrying platelet extracellular vesicles (EVs) that bind to neutrophils and promote platelet-neutrophil aggregation in lung arterioles of SCD mice in vivo and SCD human blood in microfluidics in vitro. The inflammasome activation, platelet EV generation and platelet-neutrophil aggregation were enhanced by the presence of lipopolysaccharide at a nanogram dose in SCD but not control human blood. Inhibition of the inflammasome effector caspase-1 or IL-1β pathway attenuated platelet EV generation, prevented platelet-neutrophil aggregation, and restored microvascular blood flow in lung arterioles of SCD mice in vivo and SCD human blood in microfluidics in vitro.

CONCLUSIONS: These results are the first to identify that platelet-inflammasome dependent shedding of IL-1β carrying platelet EVs promote lung vaso-occlusion in SCD. The current findings also highlight the therapeutic potential of targeting the platelet-inflammasome dependent innate immune pathway to prevent acute chest syndrome.