PARTICIPATION OF THE mTOR PATHWAY IN PLATELET ACTIVATION BY SARS-CoV-2

COVID-19 is a multisystem inflammatory disease that has been associated with a high risk for thrombotic events. Several studies have shown increased platelet activation contributing to immunothrombosis in COVID-19 patients. However, the mechanisms involved in this process have not been fully elucidated. The aim of this study was to investigate the signaling pathways activated in platelets from severe COVID-19 patients and their participation in thromboinflammatory responses to SARS-CoV-2 in vitro. Analysis of the phosphorylated proteins profile in platelets from patients with severe COVID-19 (n=3) admitted in the Instituto Estadual do Cérebro Paulo Niemeyer-Rio de Janeiro was performed (ethic committee: 30650420.4.1001.0008). Our results revealed a higher expression of phosphorylated S6K, the main effector protein of the mTOR pathway, in COVID-19 platelets compared to healthy volunteers platelets. Then, we investigated whether this pathway would be related to platelet activation by SARS-CoV-2 in vitro. Platelets from healthy donors (n=7) were stimulated with SARS-CoV-2 (MOI=0,05). Platelet activation was evaluated by expression of activation markers; adhesion and platelet spreading on fibrinogen-coated surface and secretion of inflammatory mediators. Our results demonstrated that SARS-CoV-2 activates platelets leading to increased P-selectin expression and increased release of MIF, PDGF, CD40-L and vWF. Furthermore, platelet activation triggered by the infection resulted in a larger spreading area over fibrinogen. In order to investigate whether the mTOR pathway would be involved in these processes, we incubated platelets with the mTOR inhibitor rapamycin before platelet infection. The treatment prevented platelet activation, with a reduction in P-selectin expression, decreased spreading area and lower levels of MIF and PDGF, but not of CD40-L and vWF. We conclude that SARS-CoV-2 induces platelet activation through mechanisms partially dependent on the mTOR pathway.