The Covid-19 virus would reach the brain by making small tunnels from the nose

Mental fog, memory lapses, confusion, headaches, disorientation… Since the start of the pandemic, many people have reported this type of neurological manifestation following an infection with SARS-CoV-2, especially in some cases of long Covid. If the causes behind these symptoms initially remained rather vague, autopsies carried out on deceased patients sometimes revealed the presence of the coronavirus in the brain.

However, according to previous studies, “the ACE2 receptor, which the virus normally uses to enter cells, is barely detectable in the brain, unlike the cells lining the nose, mouth and lungs”, reports New Scientist. How SARS-CoV-2 travels to the brain therefore remained a mystery. A recent study published on July 20 in the journal Science Advances, conducted by Chiara Zurzolo and her team at the Institut Pasteur, could nevertheless provide new answers.

To carry out it, the scientists decided to observe, in Petri dishes, the way in which the virus acted against two types of cells: “One, called SH-SY5Y, was used to model human brain cells; the other, Vero E6, to model the cells that line body surfaces, including the nose.”

The modeled brain cells could not, on their own, be infected with Covid-19, “because they did not have the ACE2 receptor”. However, after incubation in the same Petri dish as the cells present in the nose and which do have these receptors, “they were infected”.

A “simple and effective” mechanism

Using an electron microscope, the research team discovered that after successfully penetrating the modeled cells of the nose, “the virus has stimulated [ces dernières] so that they develop tiny tubes, called nanotubes […]which have formed connections with brain cells”. These tiny tunnels could explain how SARS-CoV-2 travels to the brain.

“I think this is a very interesting study, because it offers a simple and efficient mechanism to transfer the virus from one cell to another, without the need for ACE2 receptors”comments Frederic Meunier, from the University of Queensland, Australia, in the columns of New Scientist. “However, as the experiments were limited to cells in Petri dishes, further studies are needed to confirm that the same mechanism occurs inside the brain.”

If the virus actually circulates through these nanotubes to the brain, Chiara Zurzolo hopes that this discovery could be useful in the development of a drug to block this process. “At the moment, we don’t have a specific nanotube-blocking molecule, but we are screening to find one”she announces.

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