Pulmonary arteriole occlusion by platelet-neutrophil micro-emboli in Acute Chest Syndrome

Versiti Blood Health, Inc., Milwaukee WI

Investigators

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Abstract

PROJECT SUMMARY Acute chest syndrome (ACS) is a type of lung vascular injury and a leading cause of mortality in Sickle Cell Disease (SCD). The etiological mechanism that triggers ACS remains poorly understood and the current therapy for ACS is primarily supportive. SCD patients hospitalized with acute systemic painful vaso-occlusive episodes often develop ACS within the next few days, suggesting that molecular events surrounding lung vascular occlusion (vaso-occlusion) contribute to lung injury. This epidemiology also offers a therapeutic window to halt the development of ACS, provided targeted therapies are identified. In the last cycle of this R01, we discovered a novel P-selectin independent mechanism of ACS. We revealed that type-I interferon (type-I IFN) signaling in neutrophils promotes Gasdermin-D (GSDMD)-dependent but P-selectin-independent shedding of neutrophil extracellular traps (NETs). These NETs promote micro-embolism of precapillary pulmonary arterioles (lung vaso- occlusion) by neutrophil-platelet aggregates, leading to the arrest of blood flow and vascular injury in the lung of SCD mice. These findings have been published in Blood 2022 & 2021, Haematologica 2024, JCI-Insight 2024, Science Advances 2022, and several other articles. In the present renewal of our R01, we identify a new platelet- dependent mechanism responsible for IFN- and  (type-I IFNs) production in neutrophils, which can be targeted to prevent NETs generation and lung vaso-occlusion in SCD. Based on our new preliminary findings, we hypothesize that activation of STING signaling in platelets promotes the release of pIRF3 containing (pIRF3+) extracellular vesicles (EVs) by platelets in SCD. We also propose that these platelet-EVs transfer pIRF3 (a transcription factor) to neutrophils to promote type-I IFN production and NETs generation by neutrophils, and inhibiting STING activation in platelets will prevent development of ACS in SCD. We will test this hypothesis using our model of intravenous hemoglobin induced ACS in SCD mice, in vivo imaging of lung in live mice, in vitro microfluidic studies with patient blood, nanoparticle tracking analysis of EVs, and SCD mice genetically deficient in GSDMD or lacking IFNAR1 only in neutrophils or STING/IRF3 only in platelets. In Aim 1, we will determine whether type-I IFN production in neutrophils promotes GSDMD-dependent NETs generation and development of ACS in SCD. In Aim 2, we will determine whether delivery of pIRF3 by platelet-EVs promotes type-I IFN production in neutrophils and development of ACS in SCD. In Aim 3, we will determine whether STING activation in platelets promotes the release of pIRF3+ platelet-EVs and development of ACS in SCD. This study will introduce a novel paradigm that EV-mediated transfer of transcription factors from platelets to neutrophils promotes lung vascular injury and identify a new platelet-STING dependent mechanism of ACS in SCD.