Project Summary/Abstract More than 100 million individuals in the United States have experienced Coronavirus Disease 2019 (COVID- 19), caused by severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2). Life-threatening thrombotic events are well-described in these patients and occur in 2-3% of hospitalized patients. However, it is clear that a much greater number of patients experience microclots, small thrombotic events capable of causing localized tissue damage, and that microclots associate with the development of long-term complications from COVID-19. We hypothesize that these microclots result from a combined procoagulant and antifibrinolytic state. Through our preliminary studies we have identified two novel regulatory mechanisms that lead to the hemostatic and fibrinolytic dysfunction and microclot formation: (1) Activated endothelial cells secrete von Willebrand Factor (VWF), which binds and sequesters and inhibits protein S (PS), a critical plasma anticoagulant; and (2) dyslipidemia and elevated plasminogen activator inhibitor-1 result in sequestration and inhibition of the fibrinolytic protein tissue plasminogen activator (tPA). This combination of impaired anticoagulant and impaired fibrinolytic activity results in the formation of stable microclots, capable of blocking blood flow in microvascular beds, and causing localized hypoxia and tissue damage. We hypothesize that these dysfunctions occur during the acute phase of COVID-19 infection and persist in a sub-population of patients post-infection. As such, these mechanisms contribute to both acute and post-acute COVID- 19-associated coagulopathy. In the present study, we will test these hypotheses and extend our previous findings by following patients longitudinally from first diagnosis through 6-months post-infection, to identify the changes in the hemostatic and fibrinolytic systems, directly assess the contributions of PS and tPA to this process and their regulatory mechanisms, and determine the correlation of dysfunctions in these systems with microclot formation and recovery post-infection. Finally, we will perform similar analyses using samples from a cohort of patients with post-acute sequelae of COVID-19 (PASC), long-term complications from their initial infection. We hypothesize that these patients are individuals whose systems did not fully recover from the initial infection, and the proposed studies will allow us to compare the hemostatic and fibrinolytic systems between acute and PASC patients to evaluate this hypothesis, with particular focus on PS and tPA. The results from this study will inform on the mechanism(s) leading to COVID-19-associated coagulopathy and may determine biomarkers that can be used to identify those patients at greatest risk.

Project Narrative Blood clots are a leading cause of death in people with severe COVID-19 infection and are thought to contribute to long-term complications from COVID-19, though the causes of these clots are not clear. The goals of this project are to understand how dysfunctions in the body’s hemostatic and fibrinolytic systems lead to the formation of clots. The results will have implications for the treatment of COVID-19 patients and may provide insight into the body’s responses to other serious infections, which are commonly associated with thrombosis.