April 27 (UPI) -- COVID-19 infects both the nerve cells that power the brain and the spinal cord, which protects them, found a study presented Tuesday during the American Physiological Society annual meeting, held online due to the pandemic.
In experiments that exposed various human cells to the coronavirus, the virus attached itself to proteins on the surface of neurons, or nerve cells, which may explain how it appears to easily spread to the brain, the researchers said.
In addition, the virus also linked with proteins on the surface of astrocytes, which are cells in the spinal cord that, among other things, protect neurons from damage.
Both of these findings may provide clues as to how COVID-19 causes significant neurological damage in some patients, according to the researchers.
"While astrocytes display a higher resistance to infection, neurons seem to be more susceptible," study co-author Ricardo Costa said in a statement.
"These observations could explain why while some patients do not have any neurological symptoms, others seem to have severe ones," said Costa, a postdoctoral fellow at Louisiana State University Health in Shreveport.
Up to 10% of those infected with COVID-19 suffer brain damage during the course of their illness, research suggests.
For some, this may include symptoms such as loss of sense of taste or smell or more serious complications, such as seizures, confusion or delirium and stroke, according to Costa.
In the respiratory system, the virus is known to infect a person's cells by attaching itself to proteins on the cell surface called angiotensin-converting enzyme-2, or ACE2, receptors, Costa said.
For this study, he and his colleagues examined RNA, material found in cells that is used to carry messages between them, and proteins to determine whether human astrocytes and neurons produced ACE2.
As part of their experiments, they exposed samples of astrocytes and neurons to a version of the coronavirus that had been modified so that they could handle it safely, the researchers said.
In the experiments, both astrocytes and neurons expressed the ACE2 receptor and, as a result, both can become infected with the coronavirus, though astrocytes were less likely to become infected, they said.
Astrocytes are responsible for shuttling nutrients from the bloodstream to the neurons while keeping harmful particles out.
If they can resist infection, astrocytes could help keep the coronavirus out of the brain. However, once infected, they could easily pass the virus along to many neurons, the researchers said.
"Our findings suggest that astrocytes are a pathway through which COVID-19 causes neurological damage," Costa said.
"Only [a] few astrocytes getting infected could be sufficient for the infection to quickly spread to neurons and multiply quickly," he said.