With time going by, more and more observations are made not only on COVID-19 viral pneumonia, but also on its secondary consequences. These consequences include developing profound hyperinflammation and hypercoagulopathy with disseminated thrombogenesis and thromboembolism. There is also an increasing notion that some COVID-19 patients display severe hypoxemia without respiratory dysfunction.
Understanding if the SARS-CoV-2 attacks the vascular system directly, it is important to identify the types of vascular cells that express ACE2 receptor (the one virus binds with).
Based on a combination of clinical data, the team of scientists from Sweden hypothesizes that SARS-CoV-2 infection of pericytes is causative for the increased thrombogenicity and hypercoagulation observed in COVID-19 patients.
According to the research, ACE2 expression happens specifically and actively in pericytes. Pericytes are multi-functional mural cells of the microcurcaltion that wrap around the endothelial cells that line the capillaries and venules throughout the body. These cells are a key component of the neurovascular unit, help to sustain the blood-brain barrier, and maintain homeostatic and hemostatic brain functions.
It is important to notice, that the other cells of the neurovascular unit do not express ACE2. This data was obtained by RNA sequencing of mouse brain and lung vascular and vessel-associated cell types.
It was found that mice with lower amount of pericytes actively produce VWF (von Willebrand factor - a blood glycoprotein involved in hemostasis, such as attachment of thrombocytes to the damaged blood vessels). That concludes that SARS-CoV-2 infection of pericytes affects thrombosis.
The fact that virus infects specifically pericytes and not endothelial cells and vessels explains why people with diabetes and obesity are more likely to get infected with COVID-19. Since diabetes and obesity are harmful to endothelial barrier functions, it is easier for SARS-CoV-2 to get to pericytes.
Scientists also remind us that this is still a hypothesis, but the one that can be proven with further research. If it will be proven to be right, an effective therapy methods can be created, such as anticoagulant therapy.