CD39-carrying extracellular vesicles regulate pulmonary thrombosis in Sickle Cell Disease

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PROJECT SUMMARY Sickle cell disease (SCD) is the most common hemolytic disorder affecting African Americans. In situ (de novo) acute pulmonary thrombosis is the underlying cause in ~20% of SCD patients hospitalized with respiratory failure. The current therapy for pulmonary thrombosis in SCD is primarily supportive and a preventive therapy does not exist. Autopsy and computed tomography studies have identified that occlusion of pulmonary arterioles by platelet-rich thrombi contributes to the development of pulmonary thrombosis in SCD patients. Adenosine diphosphate (ADP) released from lysed erythrocytes activates platelets by stimulating purinergic P2Y1 and P2Y12 receptors. We recently discovered that this pathway promotes pulmonary arteriole thrombosis following acute-hemolysis in wild-type mice, suggesting that ADP-induced purinergic signaling may also promote pulmonary thrombosis in a hemolytic disorder such as SCD. However, P2Y12 receptor antagonists have shown no benefit to SCD patients in recent clinical trials, and it remains to be identified why pulmonary thrombosis develops only in a sub-set but not all SCD patients. Identifying molecular and genetic mechanisms that trigger pulmonary thrombosis in SCD, would enable the development of Precision Medicine diagnostic and therapeutic approaches for these at-risk SCD patients. Based on our new preliminary findings, we hypothesize that CD39 (ecto-nucleotidase) present in circulating extracellular vesicles (CD39+-EVs) degrades excess ADP to prevent pulmonary thrombosis in SCD, however, single-nucleotide-polymorphism (SNP) rs3176891G in the CD39- encoding gene (ENTPD1) attenuates this protection and identifies SCD patients who can benefit from anti- purinergic therapy. We will test this hypothesis using our newly developed mouse model of pulmonary thrombosis triggered by intravenous (IV) administration of ADP, in vivo imaging of lung in live mice, in vitro microfluidic studies with SCD patient blood, isolation and characterization of EVs, SCD mice genetically deficient in CD39, and genetic analyses in SCD patients with vs without SNP rs3176891G. In Aim 1, we will determine whether ADP-induced platelet aggregation and pulmonary thrombosis is impaired in SCD. In Aim 2, we will determine whether circulating CD39+-EVs degrade excess ADP to prevent pulmonary thrombosis in SCD. In Aim 3, we will determine whether SNP rs3176891G promotes pulmonary thrombosis event in SCD patients by attenuating CD39+-EVs, leading to increased ADP-induced platelet aggregation. These studies will introduce a novel paradigm that CD39+-EVs prevent pulmonary thrombosis in SCD, and establish the premise for first-ever precision medicine in SCD by identifying rs3176891G as a risk for pulmonary thrombosis.