The Covid-19 virus does infect neurons, confirms an Inserm study published in the Journal of Experimental Medicine. It seems that the virus, by infecting neurons, disrupts the vascularization of the brain, certain regions of which are then deprived of oxygen.
Brain damage proven in some patients with Covid-19
“Our results suggest that the neurological symptoms associated with Covid-19 could be linked to the consequences of the direct viral invasion of the central nervous system“, which includes the brain, the researchers say in the publication. Beyond the loss of smell and taste, some patients suffer from disorientation, confusion, memory problems, and even seizures, damaged nerves. or stroke for the more serious. A study of Lancet carried out on 60 patients shows that 55% of them still presented neurological sequelae three months after their stay in hospital.
Infected neurons deprive their neighbors of oxygen
To study the effects of SARS-CoV-2, the Covid-19 virus, on the brain, the scientists used three complementary study models: brain organoids (clumps of brain cells grown in the laboratory), mice and of the brains of patients who died from Covid-19.
By infecting the organoids, the researchers observed that the virus did indeed cause death “importantneurons. Using electron microscopy, they observed viral particles budding inside neurons. Upon closer examination, they even identify that infected neurons can influence their environment and deprive their neighbors of oxygen. Local hypoxia that could enhance the deterioration of brain tissue, already suffering from a lack of oxygen, as they observed in the brains of three deceased patients.
Injuries linked to lack of oxygen in the brains of patients
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The researchers indeed observe lesions due to “micro-ischemias”, that is to say a very localized lack of oxygen. In particular, they identify micro-ischemic infarcts, or a lack of oxygen linked to the obstruction of a blood vessel. This “suggests the possibility of ischemia and vascular abnormalities associated with neuroinvasionIn addition, a strong presence of antiviral antibodies in the cerebrospinal fluid (which bathes the brain) has suggested an immune response specifically directed to the brain in at least some patients with neurological disorders due to Covid These observations have certainly been made on only three patients, but they are confirmed by experiments on mice.
The vicious circle of neuronal invasion by Covid-19
“We demonstrate for the first time that SARS-CoV-2 neuroinvasion in mice can lead to significant remodeling of the cerebrovascular system“, announce the scientists in the publication. Clearly, the infection at the level of the brain can well remodel the blood vessels. This observation makes it possible to establish a potential link between the infection of the neurons observed in the brain organoids and hypoxia and lesions seen in the human organoid and brain of patients.
Although they cannot yet prove the cause and effect link, the researchers are formulating a hypothesis. According to them, the invasion of neurons by the Covid-19 virus can cause localized oxygen deficiencies and disrupt blood vessels to the point of creating ischemic infarcts. This localized vulnerability could in turn make the regions concerned more susceptible to viral invasion: a true vicious circle.
Future studies will have to identify how the virus invades the brain. It could be cribriform plaque, which separates the nasal cavity from the brain, an olfactory epithelium and a nerve, or the presence of the virus in the blood (viraemia).
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