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dcyphr | Evidence of the COVID-19 Virus Targeting the CNS: Tissue Distribution, Host–Virus Interaction, and Proposed Neurotropic Mechanisms

Abstract

Scientists have found that the COVID-19 virus binds to the angiotensin-converting enzyme 2 (ACE2) receptor to enter the cell. This study looks at how much ACE2 receptor is contained in the Central Nervous System (CNS) tissue. The ACE2 receptors in the CNS show if COVID-19 damages nervous tissue.


Background

COVID-19 and Genetics

The entire genome analysis of COVID-19 showed it was an RNA virus. This test also showed that COVID-19 was found before in bats in China.


ACE2 Tissue Expression

ACE2 receptors are found at high levels in the lungs, heart, kidneys, intestines, brain, and testicles. This makes these organs targets for COVID-19. Researchers also want to know the effect of COVID-19 on nervous tissue since this has not been studied as much as the other tissues listed.


ACE2 Receptors in the Brain

In other studies, SARS-CoV has caused nervous tissue death in mice when it entered through the nose. This has not been found in COVID-19, but the virus has been found in spinal fluid of deceased COVID-19 patients. Some COVID-19 patients lost their ability to breathe on their own, which may be caused by nervous tissue damage. This is all evidence that COVID-19 may interact with ACE2 receptors in the brain.


Results

How COVID-19 uses ACE2 Receptors

COVID-19 and other types of coronaviruses used a protein called the spike protein (S1). S1 allows the virus to attach to the cell membrane and uses ACE2 receptors in the process. All of the S1 proteins are very similar in their genetics, but do have some differences. The differences allow the COVID-19 S1 to bind to the human ACE2 receptor better than the other coronaviruses do. The similarities show that these coronaviruses are related in structure and evolutionary background.


How COVID-19 Enters the Brain

Since COVID-19 can travel through the blood in humans, it is likely that the virus also has the potential to penetrate the blood brain barrier. The blood moves slower around the brain than in the rest of the body, which could give COVID-19 more time to find the ACE2 receptors and bind to them. If the blood vessels near the brain get damaged from the virus, the virus has an easier time getting to the brain. If there is vessel damage, there will be bleeding around the brain. This can be fatal before the virus has had time to cause any damage to the nervous tissue. Once the virus is in the brain, it can interact with the ACE2 receptors of neurons and cause damage. COVID-19 may reach the brain through the nose before it is able to get through the blood brain barrier. This may cause damage to the CNS and may explain the loss of sense of smell in a COVID-19 patient


Conclusions

Though COVID-19 could cause fatal nervous tissue damage, the cause of most fatalities are from damage to the lungs, heart, or kidneys. But, understanding the role of COVID-19 in the nervous system could help improve treatment plans.