Covid-19: how does the virus reach the brain?

It is no longer to be proven, the Covid-19 wreaks havoc on the whole body, and the brain is not exempt.

But what scientists are now trying to understand is how does a respiratory disease manage to cause neurological symptoms?

Widely debated within the scientific community, the idea that the virus can infiltrate into the brain is defended by the Pasteur Institute. Published Wednesday, July 20 in the review Science Advancesthe study by French researchers reveals that “tunnels” present in the nose would facilitate the ascent of SARS-CoV-2 to uninfected neuronal cells.

These discoveries come to thwart previous studies having dismantled the hypothesis of a migration of the virus to brain cells, given the almost undetectable presence of the ACE2 receptor (which the virus normally uses to enter cells, as recalled by the study) in the brain.

Covid-19: migration to the brain through the nose

To reach these conclusions, researchers at the Institut Pasteur isolated two types of cells. On the one hand, SH-SY5Y, “which models brain cells”, and Vero E6, “which imitates the cells lining the surfaces of the body”, in particular the nose.

They then noticed that the brain cells alone could not be infected, lacking the ACE2 protein. But when incubated with the nasal cells, which carry the receptor, they became infected.

And that’s not all. After observation under an electron microscope, the researchers found that by stimulating the cells of the nose, the virus had promoted the development of “tiny tubes, called nanotubes, that formed connections with brain cells,” the study explains.

It is by this way that the SARS-CoV-2 would travel to the brain. “We can see the nanotubes as tunnels with a road above, which allow the infection of non-permissive cells, such as neurons, but which also facilitate the spread of infection between permissive cells”, details Chiara Zurzolo, Head of Membrane Traffic and Pathogenesis at the Institut Pasteurin a press release published on the website of the National Center for Scientific Research (CNRS).

Blocking nanotubes to limit the effects of the virus on the brain

“I think this is a very interesting study because it provides a plausible explanation for the mechanism by which the virus can be transferred from one cell to another while circumventing the need for ACE2 receptors,” said Frederic Meunier from the University of Queensland in Australia, questioned by New Scientist.

The cells having been stimulated in a small closed place by the scientists, there is a need for researchers to study the mechanism inside a human brain.

“Dr Zurzolo says his group is setting up experiments that more closely mimic the interactions between nose and brain cells,” the scientific journal informs..

“For the moment, we do not have a specific molecule blocking the nanotubessaid the researcher, but we are screening to find some and thus limit the effects of Covid-19 on the brain”.