Endothelial cells elicit a pro-inflammatory response to SARS-CoV-2 without productive viral infection

Abstract

Thrombotic and microvascular complications are frequently seen in deceased COVID-19 patients, suggesting that vascular pathology is a major driver of severe disease. However, whether this is caused by direct viral infection of the endothelium or inflammation-induced endothelial activation remains highly contentious. What role the endothelium plays in viral amplification and inflammation thus remains a key unresolved question in the pathogenesis of SARS-CoV-2. Here, we use patient autopsy samples, primary human endothelial cells and an in vitro model of the pulmonary epithelial-endothelial cell barrier to show that primary human endothelial cells express the SARS-CoV-2 receptor ACE2 and the protease TMPRSS2, albeit at low levels. Accordingly, when present in a sufficiently high concentration, SARS-CoV-2 can enter primary human endothelial cells from either the apical or basolateral surface. Whilst inducing an inflammatory response, this is not a productive infection. We further demonstrate that in a co-culture model of the pulmonary epithelial-endothelial barrier, endothelial cells are not infected with SARS-CoV-2. They do however, sense and respond to an infection in the adjacent epithelial cells, resulting in the induction of a pro-inflammatory response. Taken together, these data suggest that in vivo, endothelial cells are unlikely to be infected with SARSCoV-2 and that infection is only likely to 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 are still likely to play a key role in SARS-CoV-2 pathogenesis by sensing and mounting a pro-inflammatory response to SARS-CoV-2.

Cell-Free Hemoglobin Does Not Attenuate the Effects of SARS-CoV-2 Spike Protein S1 Subunit in Pulmonary Endothelial Cells

“…However, an important limitation with this finding is that throughout the current study, only the S1 subunit of the spike protein was used rather than live SARS-CoV-2 virus; HPAECs were treated with HbA instead of in vivo models of disease; and HbA, which readily loses heme, was evaluated rather than other Hb oxygen carriers that are less susceptible to heme loss. The use of only one viral protein instead of infectious SARS-CoV-2 virus is a limitation to this study, and also endothelial cells are not ideal for active viral replication [49]; however, our data clearly reveal that S1 protein alone can damage pulmonary endothelial cells manifested by impaired mitochondrial function and increased glycolysis coupled with pro-inflammatory cytokine release, which overall can lead to endothelial activation and loss of barrier function.…”

The SARS-CoV-2 Spike protein disrupts human cardiac pericytes function through CD147 receptor-mediated signalling: a potential non-infective mechanism of COVID-19 microvascular disease

“…(5) The link between the two conditions is not completely understood, especially in the light of the controversy about the capacity of the coronavirus to infect the vascular endothelium. (6)(7)(8)(9) While nasal and pulmonary epithelial cells are the primary target for infection, after viral replication and circulation, many other cells in distant organs, including heart resident cells, become exposed and potentially infected. Cardiac myocytes and fibroblasts express the main entry receptor angiotensinconverting enzyme 2 (ACE2), but pericytes (PCs), mural cells that support the maintenance and repair of microvasculature throughout the myocardium, (10)(11)(12) appear particularly susceptible because they reportedly express the highest levels of ACE2 in the heart.…”

Wheat Germ Spermidine and Clove Eugenol in Combination Stimulate Autophagy In Vitro Showing Potential in Supporting the Immune System against Viral Infections

“…Given that SARS-CoV-2 is transmitted through airway epithelial cells as the first gateway for viral invasion [ 35 ] and that neurological complications [ 36 ], as well as thrombotic and microvascular complications [ 37 ], are also common in patients affected by SARS-CoV-2, a human bronchial epithelial cell (HBEpiC) line, a human neuronal cell line (SHSY5Y) and a human umbilical vein endothelial cell (HUVEC) line were investigated in the present study. Moreover, given previous studies have shown that SPD plays an important role in stimulating autophagy in bronchial [ 11 ] and neuronal cells [ 27 ], the objective was to compare the effect of SPD and EUG alone and in combination on stimulating autophagy in these cell types.…”