Signaling through FcγRIIA and the C5a-C5aR pathway mediates platelet hyperactivation in COVID-19

Abstract

Patients with COVID-19 present with a wide variety of clinical manifestations. Thromboembolic events constitute a significant cause of morbidity and mortality in patients infected with SARS-CoV-2. Severe COVID-19 has been associated with hyperinflammation and pre-existing cardiovascular disease. Platelets are important mediators and sensors of inflammation and are directly affected by cardiovascular stressors. In this report, we found that platelets from severely ill, hospitalized COVID-19 patients exhibit higher basal levels of activation measured by P-selectin surface expression, and have a poor functional reserve upon in vitro stimulation. Correlating clinical features to the ability of plasma from COVID-19 patients to stimulate control platelets identified ferritin as a pivotal clinical marker associated with platelet hyperactivation. The COVID-19 plasma-mediated effect on control platelets was highest for patients that subsequently developed inpatient thrombotic events. Proteomic analysis of plasma from COVID-19 patients identified key mediators of inflammation and cardiovascular disease that positively correlated with in vitro platelet activation. Mechanistically, blocking the signaling of the FcγRIIa-Syk and C5a-C5aR pathways on platelets, using antibody-mediated neutralization, IgG depletion or the Syk inhibitor fostamatinib, reversed this hyperactivity driven by COVID-19 plasma and prevented platelet aggregation in endothelial microfluidic chamber conditions, thus identifying these potentially actionable pathways as central for platelet activation and/or vascular complications in COVID-19 patients. In conclusion, we reveal a key role of platelet-mediated immunothrombosis in COVID-19 and identify distinct, clinically relevant, targetable signaling pathways that mediate this effect. These studies have implications for the role of platelet hyperactivation in complications associated with SARS-CoV-2 infection.

Adverse Outcome in COVID-19 Is Associated With an Aggravating Hypo-Responsive Platelet Phenotype

“…However, this hypothesis requires further in-depth analysis. Although seemingly counterintuitive, our data underline previously reports showing impaired agonist responses in acutelyill COVID-19 patients relative to convalescent or healthy controls despite elevated basal activation (17,19,20,26). These findings suggest that platelet hypo-responsiveness is a common feature in COVID-19 which aggravates with disease progression and is associated with increased severity and unfavorable outcome.…”

“…The pro-inflammatory milieu in COVID-19 leads to tissue injury, endotheliopathy and extensive immune responses that could provide continuous stimulation for platelets. Indeed, plasma of severely-ill COVID-19 patients stimulates platelet degranulation (15), an effect that may involve engagement of platelet IgG receptor FcγRIIA and/or complement receptor C5aR (26). Further, platelet-activating immune complexes, potentially containing antibodies against SARS-CoV-2, were identified in critically-ill COVID-19 patients (28).…”

Platelet Phenotype Analysis of COVID-19 Patients Reveals Progressive Changes in the Activation of Integrin αIIbβ3, F13A1, the SARS-CoV-2 Target EIF4A1 and Annexin A5

“…It is also noteworthy that platelet exhaustion and hypo-responsiveness of platelets have been observed in COVID-19 patients. Platelets of COVID-19 patients show hypo-reactivity in response to in-vitro stimulation ( 9 , 29 , 30 , 32 , 33 ), indicating prior platelet hyper-activation and resulting hypo-responsiveness in COVID-19 patients ( 34 ). However, little is known about more detailed molecular changes in platelets in the context of SARS-CoV-2 infection and the course of the disease.…”

Targeting SARS-CoV-2-Platelet Interactions in COVID-19 and Vaccine-Related Thrombosis

“…Antibodies to spike protein have been found to lead to platelet activation in COVID-19 patients that was FcγRIIa-dependent (Nazy et al, 2021a). Both FcγRIIa signalling and complement formation have been found to mediate platelet activation by SARS-CoV-2 (Apostolidis et al, 2021).…”

“…An alternative approach is to target the signalling pathways of these receptors. Kinases such as Src, Syk and Btk mediate FcγRIIa-induced platelet activation and inhibitors of these kinases have been shown to prevent platelet activation by serum from a patient with vaccine-mediated thrombosis (Smith et al, 2021) and with COVID-19 (Apostolidis et al, 2021). Inhibitors of these kinases such as dasatinib (Src inhibitor), cerdulatinib (Syk inhibitor) and ibrutinib (Btk inhibitor) are already on the market as anti-cancer agents and the Syk inhibitor fostamatinib is approved for the treatment of immune thrombocytopenia (Connell and Berliner, 2019).…”