Swedish scientists have proposed an explanation of the reasons often associated with COVID-19 microvascular inflammation and coagulation disorders. It turned out that a particular type of cells the walls of blood vessels expresses the ACE2 receptor, through which the coronavirus enters into cells. The mechanism is described in an article published on the website of preprints and bioRxiv.
Analyzing the data of clinical observations of patients COVID-19, scientists noticed that many patients develop such secondary effects, viral pneumonia, deep inflammation of the blood vessels, clotting of blood clotting and thromboembolism, and severe hypoxemia — lack of oxygen in the blood, despite the fact that significant dysfunction of the lungs they have.
To understand whether making a direct contribution to the defeat of the circulatory system, the virus SARS-CoV-2, the researchers collected their own statistics for patients from Stockholm confirming that the blood clotting is a serious risk factor for COVID-19.
Using the method of sequencing RNA in single cells, the authors found that the ACE2 receptor, which binds to the virus, is actively expressed in pericytes — process the cells of the connective tissue in the walls of small blood vessels, including capillaries. However, other cells of the blood vessels — endothelial cells, perivascular macrophages and fibroblasts do not Express ACE2.
Based on these results, the researchers make the assumption that it is through pericytes the virus affects the vascular system.
The authors obtained data on the pericytes of the human heart and mice, and pericytes of vessels in the mouse brain. The same cells are in the human brain. They are involved in the regulation of blood-brain barrier, altering the lumen of the vessels.
The results showed that when a reduced number of pericytes in mice endothelial cells of microvessels become more active to produce and release a glycoprotein of blood plasma that provide the attachment of platelets to the damaged portion of the vessel. Therefore, scientists assume that the virus infection of pericytes affect the formation of blood clots.
The fact that the virus is able to strike exactly the pericytes, but not endothelial crates of blood vessels, may explain why hypertension, diabetes and obesity are risk factors for COVID-19. Under these conditions disrupted the barrier function of the endothelium, which may allows SARS-CoV-2 to penetrate to pericytes. In healthy people, they are protected by an intact endothelium, and not directly in contact with blood.
The authors stress that their hypothesis is provisional and requires validation. But if it is confirmed and it is proved that pericytes infected with the novel coronavirus, it will be clear, many of the features of the flow COVID-19, leading to dangerous complications. It will also help to develop effective therapies based on the use of anticoagulants.