ABSTRACT
Objective: Heightened inflammation, dysregulated immunity, and thrombotic events are characteristic of hospitalized COVID-19 patients. Platelets are key regulators of thrombosis, inflammation, immunity and are prime candidates for a role in the pathogenesis of COVID-19. The objective of this study was to analyze the platelet phenotype in COVID-19. Approach and Results: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is detected in human megakaryocytes and platelets in COVID-19 patients and following incubation with the virus in vitro. We show a direct interaction between SARS-CoV-2 and megakaryocytes that alters the platelet transcriptome and platelet activity. COVID-19 platelets are hyperreactive and have a distinct transcriptomic profile characteristic of prothrombotic large and immature platelets. We find transcriptomic changes mediated by SARS-CoV-2 do not occur following exposure of megakaryocytes with a coronavirus responsible for the common cold, CoV-OC43. In a cohort of 3,915 hospitalized COVID-19 patients, we analyzed blood platelet indices collected at hospital admission. Following adjustment for demographics, clinical risk factors, medication use, and biomarkers of inflammation and thrombosis, platelet count, size, and immaturity are each associated with increased critical illness and all-cause mortality. Conclusions: Our findings demonstrate that SARS-CoV-2 virions invade megakaryocytes and platelets, inducing alterations to the platelet transcriptome and activation profile, which correlate with critical illness and mortality in hospitalized COVID-19 patients.
ABSTRACT
Background : In addition to their role in thrombosis and hemostasis, platelets are key mediators of inflammation and altered immunity. Circulating monocyte-platelet aggregates (MPA) represent the crossroads between thrombosis and inflammation and may represent a therapeutic target. While antiplatelet therapy (APT) reduces platelet activity and thrombosis, its effect on MPA is uncertain. Aims : To analyze the effect of APT on MPA in vitro. Methods : The effect of different platelet-activating agonists (thromboxane analog U-46619, ADP, PAR4, collagen, and epinephrine) on MPA formation in whole blood (WB) was measured via flow cytometry. Agonist-stimulated WB was incubated in the presence of inhibitors against P-selectin, PSGL-1, PAR1 (ML161), P2Y12 (AZD1283), GPIIb/IIIa (eptifibatide), acetyl salicylic acid (ASA), and dipyridamole and assessed for MPA formation. RNA-Seq data sets of monocytes incubated with healthy platelet releasates (PR) were used to identify platelet-induced upregulation of monocyte transcripts and were validated by RT-qPCR in monocyte-PR co-incubation assays in the presence of APT. Results : Circulating MPA are increased in prothrombotic and inflammatory diseases including the most recent COVID-19. Monocytes aggregated to platelets have more CD40 and tissue factor expression than monocytes not aggregated to platelets ( P < 0.05 for each comparison). As expected, targeting P-selectin (85.4% reduction) and PSGL-1 (88.2% reduction) had the greatest attenuation of MPA. Among platelet inhibitors, P2Y12 inhibition was most effective in lowering MPA formation (30.7% reduction) (figure 1). Flow cytometry analysis of MPA. Incubation of monocytes with platelet releasate induced upregulation of inflammatory mRNA transcripts suppressor of cytokine signaling 3 ( SOCS3 ) and o ncostatin m ( OSM ). Following pretreatment of platelets with APT, both GPIIb/IIIa and P2Y12 inhibition was associated with lower expression of SOCS3 and OSM (figure 2) . SOCS3 and OSM in monocytes incubated with APT-treated PR. Conclusions : Circulating MPA represent a crossroad of platelet and monocyte activation. We show that APT is associated with both reduced MPA formation and platelet-induced monocyte activation.