Effects of Viral Infection on Endothelial Activation and Barrier Function
Authors: Yazdanparast Tafti Sajedehalsadat , Rivera Gonzalez Xaymara , Zhang Xiaohui 
Published: May 2022

Endothelial cells (ECs) are in the inner layer of blood vessels, and it controls the transportation of nutrition and essential molecules from the extracellular matrix to the intracellular space making a homeostasis environment. Vascular endothelium can be disrupted with viruses, which are among the main reasons for epidemic and pandemic outbreaks, and it leads to health issues such as cardiovascular‐related diseases. Wide range of viruses can potentially target the endothelium including Dengue virus estimated to infect 390 million people per year. Zika virus leads to pregnancy complications such as preterm birth and miscarriage. Tick‐borne encephalic damaged the central nervous system and, Hantavirus has a mortality rate of 38% through hantavirus pulmonary syndrome. Reviewing these several diseases, including SARS‐CoV‐2, has given an in‐depth look at what the endothelial cells are going through when these viruses are infecting the host bodies. Following the virus infection, ECs are going through activation mode, which is accompanied with glycocalyx degradation, plasma leakage, phosphorylation of P120, and cadherin, increased proinflammatory responses and, disruption of barrier integrity.

The SARS‐CoV‐2 pandemic has taken a global toll; With a total of 362 million cases, there are 5.63 million deaths occurring. With the usage of immunofluorescence and vascular permeability assay, we monitor how Human Umbilical Vascular Endothelial Cells (HUVEC) and Human Lung Microvascular Endothelial Cells (HLMVEC) are impacted when treated with UV‐inactivated & heat‐inactivated SARS‐CoV‐2, and tumor necrosis factor (TNF)‐α. TNF‐α is an inflammatory cytokine prominent during inflammation and its known to increase the permeability of endothelium. Like the TNF‐α, both cells treated with UV‐inactivated and heat‐inactivated SARS‐CoV2 demonstrated boosted permeability. With the considerable effect of SARS‐CoV2 on the permeability of ECs, it is essential to understand the mechanisms and pathways behind the boosted leak, including the impact of the virus on the expression of adhesion molecules like platelet endothelial cell adhesion molecule (PECAM‐1). One can see in the images of HUVEC and HLMVEC that SARS‐CoV‐2 diminish the localization of PECAM‐1. On a non‐treated negative control, cells are spaced evenly and are close to another since their junctions are not targeted. Once the cells are treated with either heat‐inactivated or UV‐inactivated SARS‐CoV‐2, PECAM‐1 localization is disrupted, which can be seen from the space between cells since the PECAM‐1 has been altered and is no longer holding the cells together. From those exact images, one can detect the enlarged and irregular shapes of nucleuses and change in morphology of these cells since the SARS‐CoV‐2 is not only altering the PECAM‐1 complex but it can also modify various proteins and mRNAs. By combining information of various viruses and knowledge from our studies, we can understand the mechanisms of ECs and take measurements to protect ECs from viruses. In future experiments, we will detect if the PECAM‐1 expression is lowered when treated with SARS‐CoV‐2 and TNF‐α or if PECAM‐1 is internalized in the cell. Moreover, we can do mRNA and immunoblotting analysis to elaborate the changes in protein pathways as a consequence of COVID‐19.