Liver-to-lung microembolic NETs promote gasdermin D–dependent inflammatory lung injury in sickle cell disease

Abstract

Acute lung injury, referred to as the acute chest syndrome, is a major cause of morbidity and mortality in patients with sickle cell disease (SCD), which often occurs in the setting of a vaso-occlusive painful crisis. P-selectin antibody therapy reduces hospitalization of SCD patients by almost 50%, suggesting that an unknown P-selectin-independent mechanism promotes remaining vaso-occlusive events. In SCD patients, intra-erythrocytic polymerization of mutant hemoglobin promotes ischemia-reperfusion injury and hemolysis, which leads to the development of sterile inflammation. Using intravital microscopy in transgenic, humanized SCD mice and in vitro studies with blood from SCD patients, we reveal for the first time that the sterile inflammatory milieu in SCD promotes caspase-4/11-dependent activation of neutrophil-Gasdermin-D (GSDMD), which triggers P-selectin-independent shedding of neutrophil extracellular traps (NETs) in the liver. Remarkably, these NETs travel intravascularly from liver to lung, where they promote neutrophil-platelet aggregation and the development of acute lung injury. This study introduces a novel paradigm that liver to lung embolic translocation of NETs promotes pulmonary vascular vaso-occlusion, and identifies a new GSDMD-mediated, P-selectin-independent mechanism of lung injury in SCD.

Thrombo-inflammation in COVID-19 and Sickle Cell Disease: Two Faces of the Same Coin

“…Consistent with the above, incubation of human peripheral neutrophils with VOC plasma produced significantly more NETs compared to nonsickle and steady-state plasma [68]. NET generation in SCD is caused by sterile inflammation [62]. Additionally, during SCD-induced bone marrow infarction, the bone marrow undergoes stress reticulocytosis.…”

“…2). Cell-free heme also amplifies inflammation [66] by activating inflammatory pathways including TLR signaling [67], gasdermin D-dependent NET formation [60,62], plateletinflammasome activation and generation of IL-1β carrying platelet extracellular vesicles and priming of the inflammasome, leading to platelet-neutrophil aggregation and vasoocclusion [29,52]. Consistent with the above, incubation of human peripheral neutrophils with VOC plasma produced significantly more NETs compared to nonsickle and steady-state plasma [68].…”

“…Intravascular release of tissue factor (TF) also contributes to the polarization toward a prothrombotic state [24,[56][57][58]. Release of cell-free heme activates converging inflammatory pathways, such as TLR4 signaling [59], formation of neutrophil extracellular traps (NETs) [25,60] and priming of the inflammasome (NLRP3) pathway, leading to release of interleukin-1β (IL-1β) and IL-18 by leukocytes, platelets, and endothelial cells, which contributes to the development of a sterile thrombo-inflammatory state in SCD [29,52,61,62].…”

“…Platelet-inflammasome activation led to the generation of IL-1β and caspase-1-carrying platelet extracellular vesicles 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 [29]. Inhibition of the inflammasome effector More recent findings show that sterile inflammation in SCD promotes caspase-11/4-dependent activation (cleavage) of pyroptotic effector gasdermin-D (GSDMD) in neutrophils, which leads to generation of NETs in the liver [62]. These NETs embolize from the liver to the lung to promote P-selectin-independent lung vaso-occlusion in SCD [62].…”

“…Inhibition of the inflammasome effector More recent findings show that sterile inflammation in SCD promotes caspase-11/4-dependent activation (cleavage) of pyroptotic effector gasdermin-D (GSDMD) in neutrophils, which leads to generation of NETs in the liver [62]. These NETs embolize from the liver to the lung to promote P-selectin-independent lung vaso-occlusion in SCD [62]. Interestingly, GSDMD is highly expressed on the BALF and blood neutrophils of COVID-19 patients.…”