The ACE2 Receptors
Could this explain why some are more susceptible to COVID-19?
The SARS-CoV-2 virus gains entry to the epithelial cells lining the respiratory tract by way of the ACE2 (angiotensin-converting enzyme 2) receptor. This is the protein to which the viral spike proteins attach in order to gain entry into the cell.
If we knew more about this important receptor, it could be the key to unlock future therapies and preventive measures.
This ACE2 receptor is a transmembrane protein, in that it is embedded in the cell membrane. This protein is found on epithelial and endothelial cells of the upper and lower respiratory tract, heart and vasculature, kidneys, and portions of the gastrointestinal tract. It is an ectoenzyme, meaning its actions occur outside of cells. The ubiquitous nature of this receptor explains, in part, why so many different organs can be affected by SARS-CoV-2.
ACE2 is a vital element in a biochemical pathway that is critical to regulating processes such as blood pressure, wound healing and inflammation, called the renin-angiotensin-aldosterone system (RAAS) pathway.
Why are children so rarely affected by the disease?
ACE2 is present in all people but the quantity can vary among individuals and in different tissues and cells. Some evidence suggests that ACE2 may be higher in patients with hypertension, diabetes and coronary heart disease. This may explain why these patient groups are more prone to serious COVID-19 disease. The ACE2 receptor concentration in the cell membranes may also explain why children are less susceptible to serious COVID-19 disease. It is known that children have less ACE2 receptors in their tissues. Also, their ACE2 receptors have less maturity and functionality while having less expression and affinity to invading viruses.
Researchers have also found that ACE2 lung airway expression is upregulated and intensified in smokers and those with COPD (chronic obstructive pulmonary disease.)
When the amount of ACE2 is reduced because the virus is occupying the receptor sites, individuals may be more susceptible to severe illness from COVID-19 thus increasing susceptibility to inflammation, cell death and organ failure, especially in the heart and the lung.
Currently, clinical trials are being conducted to determine if ACE inhibitors could be effective in treating COVID-19. Undoubtedly, the extensive research being conducted on this topic will eventually bring exciting news and relief to many.
