SARS-CoV2 spike protein can activate platelets through integrin alpha iib beta 3

Background : Patients with severe coronavirus disease 19 (COVID-19) are at increased risk of thrombosis, which can be a challenge to manage and is associated with elevated mortality. The virus responsible for COVID19, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV2), is unique amongst coronaviruses that infect humans in that its envelope spike protein includes an arginine-glutamateaspartate (RGD) peptide sequence in its receptor-binding domain (RBD). In platelets, RGD sequences are recognised by the main platelet activation and adhesion integrin, α IIb β 3 , triggering integrin activation, outside-in signalling, and platelet activation. Aims : To investigate whether the RGD sequence in the spike protein is able to activate platelets through integrin a IIb b 3 . Methods : Fibrinogen, collagen, purified spike and RBD protein were coated on glass slides and platelets were allowed to adhere under static or flow conditions. Slides were washed, stained platelets with ActinGreen and imaged by confocal microscopy. Results : Purified SARS-CoV2 spike protein and RBD protein triggered platelet spreading and this was blocked by incubating the platelets with the clinically used non-peptide RGD mimetic α IIb β 3 -integrin blocker, tirofiban. In an in vitro thrombosis model using healthy donor blood, we find surprisingly that this ability to activate platelet integrins does not translate into an enhancement in thrombus formation on collagen, and platelets cannot form thrombi on the spike protein under arterial or venous conditions. Conclusions : We conclude therefore that although SARS-CoV2 spike contains an RGD sequence that can activate platelet integrins, whether this contributes to enhanced thrombosis under pathological conditions in Covid-19 patients is not known. Structural analysis of the RGD site suggests a buried location in the spike, which may be revealed by other activatory mechanisms and receptors, and which will require further study.