Differential effects of SARS-CoV-2 variants on central nervous system cells and blood–brain barrier functions, 2023, Proust et al

[EndME]

Differential effects of SARS-CoV-2 variants on central nervous system cells and blood–brain barrier functions


Background

Although mainly causing a respiratory syndrome, numerous neurological symptoms have been identified following of SARS-CoV-2 infection. However, how the virus affects the brain and how the mutations carried by the different variants modulate those neurological symptoms remain unclear.

Methods
We used primary human pericytes, foetal astrocytes, endothelial cells and a microglial cell line to investigate the effect of several SARS-CoV-2 variants of concern or interest on their functional activities. Cells and a 3D blood–brain barrier model were infected with the wild-type form of SARS-CoV-2, Alpha, Beta, Delta, Eta, or Omicron (BA.1) variants at various MOI. Cells and supernatant were used to evaluate cell susceptibility to the virus using a microscopic assay as well as effects of infection on (i) cell metabolic activity using a colorimetric MTS assay; (ii) viral cytopathogenicity using the xCELLigence system; (iii) extracellular glutamate concentration by fluorometric assay; and (iv) modulation of blood–brain barrier permeability.

Results
We demonstrate that productive infection of brain cells is SARS-CoV-2 variant dependent and that all the variants induce stress to CNS cells. The wild-type virus was cytopathic to all cell types except astrocytes, whilst Alpha and Beta variants were only cytopathic for pericytes, and the Omicron variant cytopathic for endothelial cells and pericytes. Lastly wild-type virus increases blood–brain barrier permeability and all variants, except Beta, modulate extracellular glutamate concentration, which can lead to excitotoxicity or altered neurotransmission.

Conclusions
These results suggest that SARS-CoV-2 is neurotropic, with deleterious consequences for the blood–brain barrier integrity and central nervous system cells, which could underlie neurological disorders following SARS-CoV-2 infection.




https://jneuroinflammation.biomedcentral.com/articles/10.1186/s12974-023-02861-3

 

[rvallee]

The wild-type virus was cytopathic to all cell types except astrocytes, whilst Alpha and Beta variants were only cytopathic for pericytes, and the Omicron variant cytopathic for endothelial cells and pericytes

This is seriously wild. Despite having completely botched the pandemic, medicine will progress massively from it. It could have regardless, but this really all confirms to me the general pattern that learning, even scientific learning, only happens by accident, by exploring all the spaces. It's a brute force thing where individual skill is almost meaningless, it mostly needs scale and resources to look everywhere, probably multiple times. And time. And I guess literally making all the mistakes. Again and again. Intelligence truly is a social emergent phenomenon.

 

[SNT Gatchaman]

We showed that susceptibility and permissivity to the viruses was variant dependent and that they all induced stress in CNS cells, the outcome of which depended on the variant and cell type. Also, using an in vitro BBB model, we demonstrated that WT virus increases BBB permeability and that all variants, except Beta, modulate extracellular glutamate levels.

The concentration of the neurotransmitter glutamate in the extracellular space is tightly regulated to prevent excitotoxicity. This homeostasis is mainly maintained by astrocytes which take up and release glutamate. Considering that (i) astrocytes support the integrity of the BBB, (ii) astrocytes are productively infected by some SARS-CoV-2 variants and (iii) the metabolic activity of astrocytes is affected by SARS-CoV-2 infection, we therefore investigated the effect of SARS-CoV-2 on extracellular glutamate in our BBB model.

shows that WT, Alpha, and Eta variants at high MOI transiently increased extracellular glutamate, with a peak at day 4. [...] Interestingly, Omicron infection induced a decrease in extracellular glutamate until reaching the uninfected condition at day 6

Similarly to us, they showed an infection of microglia by all the tested variants. However, they saw no infection of astrocytes which is discordant from our work

Despite the function of the BBB to restrict ingress of circulating microorganisms, it has been suggested that SARS-CoV-2 could infiltrate the BBB as cell-free viral particles, either by a transcellular pathway (through cells, with or without replication in endothelial cells), or a paracellular passive diffusion across a more permeable BBB (between cells).

An increase of BBB permeability could lead to lymphocyte, monocyte and neutrophil migration into the brain which could induce neuroinflammation, ROS production, microglial and astroglial activation, oligodendrocyte dysfunction or myelin damage, thereby contributing to neurological disorder

Glutamate is the major excitatory neurotransmitter in the mammalian CNS and its concentration in the brain is tightly regulated, with both too little and too much glutamate being harmful, both can lead to defects in neurotransmission (too little glutamate) and excitotoxicity (too much glutamate). Excitotoxicity, reported to be involved in neurodegenerative disorders in humans, can occur acutely when mediated by the increase of extracellular glutamate levels.

(cf FND / "functional seizures")

Altogether, our work suggests that SARS-CoV-2 affects the normal physiological functions of the BBB and its cellular components and thus contributes to the wide spectrum of neurological manifestations of SARSCoV-2 that have been observed clinically. More specifically, our results demonstrate that the WT virus and the Omicron variant may have a higher potential for neurological damage due to their ability to induce CNS cell stress, affect extracellular glutamate concentration, and damage BBB cellular components.