SARS-CoV-2 endothelial disease stimulates proinflammatory responses without supporting viral expansion, study finds

A team of scientists from Australia and Brazil recently studied the involvement of endothelial cells in the pathogenesis of acute respiratory disease coronavirus syndrome 2 (SARS-CoV-2). The study concludes that endothelial cells are less susceptible to SARS-CoV-2 disease unless there are high viral loads in the blood or basolateral epithelial disease. However, these cells can significantly contribute to the pathogenesis of SARS-CoV-2 by stimulating proinflammatory responses. The study is currently available on the bioRxiv* preprint server.

Background

SARS-CoV-2, the causative pathogen of coronavirus 2019 (COVID-19), has been found to cause severe lung and cardiovascular complications, especially in susceptible individuals. Being a respiratory virus, SARS-CoV-2 essentially attacks lung epithelial cells before exposure to lung endothelial cells. In the context of COVID-19-related cardiovascular pathologies, some autopsy studies have identified viral RNA in the vascular network of many organs, but some studies have failed endothelial disease directly with SARS- CoV-2.

Because endothelial cells are known to express angiotensin-converting enzyme 2, which is the host cell receptor for SARS-CoV-2 ingestion, it is theoretically possible to induce SARS-CoV-2 infection. endothelial. There is a growing body of evidence suggesting that infection-induced SARS-CoV-2 infection of the lung epithelial barrier may lead to endothelial disease directly through the basolateral side of the epithelial lining, located next to the lung endothelial layer.

In the present study, the scientists aim to investigate whether COVID-19-related inflammatory pathologies are caused by direct endothelial disease or inflammation-induced endothelium activity.

Study design

To study the SARS-CoV-2-induced changes in the endothelial cells in vivo, the scientists collected lung tissue samples from 10 COVID-19 patients who died and stained for the mRNA spike of SARS-CoV-2. In addition, they did a series of in vitro studies using primary human endothelial cells and an experimental model of the lung epithelial-endothelial cell barrier to assess the pathogenesis of SARS-CoV-2.

Important comments

According to the in vivo conclusions, no spike mRNA was detected in the lung livers. This indicates that SARS-CoV-2 does not directly affect lung endothelial cells. Moreover, the conclusions of the in vitro Tests showed that primary human endothelial cells expressed mRNAs of both ACE2 and TMPRSS2 (host cell protease required for spike priming) and that expression rates were comparable to those observed in human epithelial cell line (Calu-3). However, at the protein level, significantly lower expressions of ACE2 and TMPRSS2 were observed in endothelial cells compared to that in epithelial cells. These observations indicate that, compared with epithelial cells, endothelial cells are less susceptible to SARS-CoV-2 infection due to lower expression levels of ACE2 and TMPRSS2.

To further investigate the potential for endothelial disease, the scientists tested primary endothelial cells with SARS-CoV-2 either apically or basolaterally. Apical infection occurs when the virus is present in the bloodstream, and basolateral infection occurs when the virus is present in the basolateral surface of the adjacent epithelial lining. However, in both cases of infection, they found no sign of viral reproduction within these cells. Furthermore, they did not detect the SARS-CoV-2 nuclear protein in these cells. Importantly, no morphological change was observed in endothelial cells after SARS-CoV-2 infection.

By increasing the amount of SARS-CoV-2 for experimental disease, they observed a greater increase of viral nuclear proteins in endothelial cells. However, no viral reproduction was identified. These observations show that, although SARS-CoV-2 can enter endothelial cells when present at high concentrations, it cannot reproduce to induce reproductive disease.

To study inflammatory responses of SARS-CoV-2 infectious endothelial cells, they measured the expression of intercellular adhesion molecules 1, which is known to be stimulated in endothelial cells in response to inflammation. In addition, they assessed whether infectious endothelial cells secrete proinflammatory cytokines. By performing immunofluorescence staining and biochemical assays, they observed increased expression of intercellular adhesion molecules 1 and strong secretion of interleukin 6 (IL-6) in endothelial cells with SARS-CoV-2 either apically or basolaterally . These observations indicate that, although it causes infectious disease, SARS-CoV-2 can induce inflammatory responses in endothelial cells.

Introducing a more rational co-cultivation model of the lung epithelial-endothelial barrier with SARS-CoV-2, they found that, unlike epithelial cells, which clearly showed signs of infection, they did not endothelial cells expressed viral nuclear protein or RNA infection. . On further analysis, they found that endothelial cells responded to the infection in the adjacent epithelial cells by inducing secretion of proinflammatory mediators.

Investigate meaning

The study shows that endothelial cells are susceptible to SARS-CoV-2 infection only when the virus is present in the nearby basolateral epithelial surface or when it is present in the circulation in quantities very high. Even if SARS-CoV-2 enters endothelial cells, the disease is associated only with inflammatory responses and not with viral expansion.

* Important message

bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be seen as final, guiding health-related clinical / behavioral practice, or treated as fixed information.