SARS-CoV-2 ORF7a activates the endothelium to release von Willebrand factor that promotes thrombosis.

BACKGROUND: Patients with severe and critical COVID-19 frequently exhibit thromboembolic complications, a significant cause of mortality and morbidity. Increased plasma levels of von Willebrand factor (VWF) following SARS-CoV-2 infection have been extensively reported, which links to thrombosis and increased mortality. However, the mechanism underlying SARS-CoV-2-associated thrombotic complications is not fully understood. OBJECTIVES: To determine the mechanism of SARS-CoV-2-associated thrombosis. METHODS: Drosophila genetic screening and molecular, cellular, and biochemical approaches were used. RESULTS: Genetic screening identified a SARS-CoV-2 accessory protein, Orf7a, as a crucial factor promoting agglutination of hemolymph, the circulatory fluid of flies, which is functionally comparable to the blood and lymph of vertebrates. Further studies using cultured murine splenic vascular endothelial cells and human umbilical cord endothelial cells demonstrated that overexpression of ORF7a in these cells significantly activated and stimulated the release of VWF, leading to an increased rate and final coverage of Adamts-13 (-/-) murine platelets on activated endothelial surfaces under arterial shear. Moreover, a soluble recombinant ORF7a could also activate human endothelial cells and trigger the release of VWF from Weibel-Palade bodies. CONCLUSION: We demonstrate for the first time that SARS-CoV-2 ORF7a may be one of the pathogenic factors contributing to COVID-19-associated thrombosis by activating the vascular endothelium to release ultralarge VWF, which promotes platelet adhesion and agglutination, and thrombus formation. Thus, a strategy specifically targeting VWF-platelet interaction, such as recombinant a disintegrin and metalloprotease with thrombospondin type 1 repeats, 13 (ADAMTS-13) and/or caplacizumab, may be efficacious in reducing COVID-19-associated thrombosis and mortality.