Endothelial cells are not productively infected by SARS‐CoV‐2

Abstract

ObjectivesThrombotic and microvascular complications are frequently seen in deceased COVID‐19 patients. However, whether this is caused by direct viral infection of the endothelium or inflammation‐induced endothelial activation remains highly contentious.MethodsHere, we use patient autopsy samples, primary human endothelial cells and an in vitro model of the pulmonary epithelial–endothelial cell barrier.ResultsWe show that primary human endothelial cells express very low levels of the SARS‐CoV‐2 receptor ACE2 and the protease TMPRSS2, which blocks their capacity for productive viral infection, and limits their capacity to produce infectious virus. Accordingly, endothelial cells can only be infected when they overexpress ACE2, or are exposed to very high concentrations of SARS‐CoV‐2. We also show that SARS‐CoV‐2 does not infect endothelial cells in 3D vessels under flow conditions. We further demonstrate that in a co‐culture model endothelial cells are not infected with SARS‐CoV‐2. Endothelial cells do however sense and respond to infection in the adjacent epithelial cells, increasing ICAM‐1 expression and releasing pro‐inflammatory cytokines.ConclusionsTaken together, these data suggest that in vivo, endothelial cells are unlikely to be infected with SARS‐CoV‐2 and that infection may only occur if the adjacent pulmonary epithelium is denuded (basolateral infection) or a high viral load is present in the blood (apical infection). In such a scenario, whilst SARS‐CoV‐2 infection of the endothelium can occur, it does not contribute to viral amplification. However, endothelial cells may still play a key role in SARS‐CoV‐2 pathogenesis by sensing adjacent infection and mounting a pro‐inflammatory response to SARS‐CoV‐2.

Organoid Models of SARS-CoV-2 Infection: What Have We Learned about COVID-19?

“…Nonetheless, the extent to which the direct infection of endothelial cells by SARS-CoV-2 contributes to vascular involvement in COVID-19 remains to be determined and may indeed be organ and tissue dependent. In vitro cultures of primary human umbilical vein endothelial cells (HUVECs) and human microvascular endothelial cells from the lung (HMVEC-L) did not support SARS-CoV-2 infection [157]. These HUVECs and HMVES-L cells expressed very low levels of ACE2 and TMPRSS2 and did not show any morphological changes upon virus exposure to their apical or basal surface.…”

COVID-19 and the Vasculature: Current Aspects and Long-Term Consequences

“…For instance, transwell filter systems allow for initiation of the viral infection via different compartments, namely apical and basolateral. The study of Schimmel et al (2021) showed that the virus cannot actively replicate in umbilical cord and microvascular endothelial cells, but SARS-CoV-2 is able to enter the cell via either the apical or basolateral side ( Schimmel et al, 2021 ). Moreover, a pro-inflammatory response of the cells was observed, indicative of an interaction of the virus with the cells.…”

“…In addition, the endothelial cells are exposed to shear stress in vivo , and therefore employing microfluidic devices is a potentially interesting technique mimicking the natural vascular environment. Endothelial cells that were seeded in a polydimethylsiloxane (PDMS) channel containing a collagen hydrogel were infected under flow, but also this method did not allow for viral replication of SARS-CoV-2 in the endothelial cells ( Schimmel et al, 2021 ). This is an interesting finding since it has been described that shear stress could upregulate ACE2 expression in brain microvascular endothelial cells, thereby allowing for attachment of the S protein, as shown in ( Kaneko et al, 2021 ) Figure 3 .…”

Carbon dioxide inhibits COVID-19-type proinflammatory responses through extracellular signal-regulated kinases 1 and 2, novel carbon dioxide sensors

“…S3a). SARS-CoV-2 is able to infect human blood vessel organoids and ECs in vitro without undergoing viral replication and induces a clear proinflammatory response [ 17 ]. Therefore, we were able to demonstrate that in ECs, ERK1/2 activity in response to 40 ng/ml RBD increased gradually up to ~ 30% after 24 h (Fig.…”