Endothelial progenitors exhibit a senescent and prothrombotic phenotype post COVID-19 disease

<b>Background:</b> COVID-19 is associated with long-term risk of cardiovascular disease (CVD), particularly after severe disease. The long-term consequences of SARS-CoV-2 infection on endothelium are poorly understood. Senescent endothelial cells are dysfunctional, exhibit a proinflammatory 'senescence-associated-secretory-phenotype' (SASP) and promote CVD. We hypothesised that endothelium post-COVID is senescent and dysfunctional, promoting cardiovascular comorbidities. <b>Methods:</b> Endothelial colony forming cells (ECFC) are circulating endothelial progenitors and provide non-invasive access to endothelial cells. We collected blood samples from individuals who recovered from COVID-19 (n=6, 8-13 months post infection, 5 had critical disease) and age-matched healthy controls for ECFC isolation. ECFC were characterised for endothelial markers, proliferation, senescence and selected SASP mediators by immunofluorescence (IF). We used a high-throughput 'organ-on-a-chip' microfluidic platform (OrganoPlate-MIMETAS) that allows formation of microvessels for functional and IF analysis. <b>Results:</b> Post-COVID ECFC exhibited reduced proliferation (Ki-67), increased expression of senescence markers (senescence-associated-β-galactosidase activity, p21), IFN-γ-inducible-protein-10, plasminogen activator inhibitor-1 and von Willebrand Factor compared to control ECFC. In 3D cultures maintained for 14 days, microvessels formed with post-COVID ECFC showed increased permeability and disruption of endothelial junctions. <b>Conclusion:</b> We demonstrate that ECFC from patients post-COVID exhibit a dysfunctional, senescent and prothrombotic phenotype that may contribute to the increased risk of cardiovascular comorbidities.