SARS-CoV-2 Spike Protein Accumulation in the Skull-Meninges-Brain Axis: Potential Implications for Long-Term Neurological Complications

SNT Gatchaman

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SARS-CoV-2 Spike Protein Accumulation in the Skull-Meninges-Brain Axis: Potential Implications for Long-Term Neurological Complications in post-COVID-19
Zhouyi Rong; Hongcheng Mai; Saketh Kapoor; Victor Puelles; Jan Czogalla; Julia Schaedler; Jessica Vering; Claire Delbridge; Hanno Steinke; Hannah Frenzel; Katja Schmidt; Oezuem Sehnaz Caliskan; Jochen Martin Wettengel; Fatma Cherif; Mayar Ali; Zeynep Ilgin Kolabas; Selin Ulukaya; Izabela Horvath; Shan Zhao; Natalie Krahmer; Sabina Tahirovic; Ali Oender Yildirim; Tobias Huber; Benjamin Ondruschka; Ingo Bechmann; Gregor Ebert; Ulrike Protzer; Harsharan Singh Bhatia; Farida Hellal; Ali Erturk

Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), has been associated mainly with a range of neurological symptoms, including brain fog and brain tissue loss, raising concerns about the virus's acute and potential chronic impact on the central nervous system.

In this study, we utilized mouse models and human post-mortem tissues to investigate the presence and distribution of the SARS-CoV-2 spike protein in the skull-meninges-brain axis.

Our results revealed the accumulation of the spike protein in the skull marrow, brain meninges, and brain parenchyma. The injection of the spike protein alone caused cell death in the brain, highlighting a direct effect on brain tissue. Furthermore, we observed the presence of spike protein in the skull of deceased long after their COVID-19 infection, suggesting that the spike's persistence may contribute to long-term neurological symptoms. The spike protein was associated with neutrophil-related pathways and dysregulation of the proteins involved in the PI3K-AKT as well as complement and coagulation pathway.

Overall, our findings suggest that SARS-CoV-2 spike protein trafficking from CNS borders into the brain parenchyma and identified differentially regulated pathways may present insights into mechanisms underlying immediate and long-term consequences of SARS-CoV-2 and present diagnostic and therapeutic opportunities.

Link | PDF (Preprint: BioRxiv)
 
Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), has been associated mainly with a range of neurological symptoms, including brain fog and brain tissue loss, raising concerns about the virus's acute and potential chronic impact on the central nervous system.
That's a first sentence that might raise a few eyebrows from respiratory physicians, I'm not sure that that is what they meant.

I find this quite interesting. Viral persistence with long periods of latency would be a straightforward answer to the question 'what causes ME/CFS?'. I think it is possible.

A summary of previous evidence for persistence:
However, the long persistence of the spike protein has been shown in the patient’s immune cells (at least 15 months)30 and in the patient’s blood plasma (at least 12 months in a preprint)31. Radio- labeled free spike protein has been shown to cross mice’s blood-brain barrier and enter the brain parenchyma32. However, due to the limited resolution of the methods employed, the exact routes of spike protein entry to the brain, their targets, and molecular changes associated with spike protein accumulation in brain tissue remain largely unclear33,34.


Whole body distribution of spike S1 protein in a mouse model
They fluorescently-labelled spike protein that binds to the mouse version of the ACE receptor and injected it into mice. After 30 minutes, they looked for the fluorescence. It sounds as though it was mostly in or very close to the blood vessels, as we might expect, but also in testes, ovaries and the brain and spinal column, skull marrow niches, in the channels connecting the skull marrow to the meninges, and other bone marrow niches (e.g.in the tibia and femur). Control proteins of the spike protein that binds to the human ACE receptor and a flu protein were not distributed throughout the body like this.

So, that tells us that the spike protein can get into most parts of mice pretty quickly, although it doesn't tell us about persistence.
 
SARS-CoV-2 infection in the human skull, meninges, and brain
They found viral spike protein in the skull marrow niches, skull marrow channels, and meninges of 17 patients who died during an acute Covid-19 infection and no viral spike protein in samples from control patients. They suggest that the spike protein leaked into the bone marrow. They also found spike protein in the perinuclear space of meningeal cells and around neurons in the brain cortex.

They identified SARS-coV2 RNA and nucleocapsid protein in about half each of the skull samples and meninges samples.

So, very good evidence that the the virus and viral proteins are getting into human skulls and meninges, but still not evidence that they persist.
 
So far, this is a nicely written paper - it's quite straightforward for such technical things.
From a German team.

Proteomics profiling of COVID-19 patient skull marrow, meninges, and brain samples
They compared the proteins in the skull and brain tissues of 10 Covid-19 patients and 10 non-Covid patients, reporting similar sets of proteins within each group, but less similarities between the groups.
suggesting a substantial and reproducible influence of the viral infection on the protein expression profiles in the skull marrow.
Here's the PCA analysis of the Covid and non-Covid protein sets
Screen Shot 2023-04-06 at 7.28.16 pm.png
When they looked at the proteins that were different in the Covid-19 nonsurvivors' bone marrow, meninges and brain cortex, they found a whole lot associated with a viral infection and immune responses. There is detail there that looks like novel findings, potentially useful for managing acute infections. They do mention NDUFA proteins, noting loss or dysfunction of these problems can impair mitochondrial function, suggesting this might be relevant to the symptom of chronic fatigue.

We identified several dysregulated proteins associated with neurodegeneration, such as downregulation of MBP and upregulation of GFAP. GFAP has been described as a biomarker to detect damage in the blood-brain barrier leading to brain injury during COVID-19 infection76. GRIA1 is a glutamate receptor subunit associated with neurodevelopmental disorders, and its deletion in mice causes attention deficit and sleep disorder, both reported symptoms of post-COVID syndrome77–80. NDUFA3 is a subunit of the mitochondrial membrane respiratory chain associated with Alzheimer’s disease81. We found NDUFA2 and NDUFA3 were dysregulated in the spike protein-positive regions (Fig. 3J). To our knowledge, their role in COVID-19 pathogenesis has not been investigated in detail yet.However, their decrease or loss of function significantly impairs mitochondrial function82, a source of oxidative stress also reported in SARS-CoV-2 infection83 and long- term symptoms such as chronic fatigue84.
 
Spike S1 protein triggers proteomics changes in the mouse skull marrow, meninges, and brain
They did similar sorts of things with the mice, looking at proteins in the skull and brain tissues 3 days after the injection of the spike protein or controls. As in the human tissues, they found proteins involved in immune responses, namely NETs formation, neutrophil degranulation and PI3K-AKT pathways. In the mouse brain cortex exposed to the spike protein, they found proteins associated with neurodegeration. NDUFA makes an appearance.
These data suggest that the SARS-CoV-2 spike S1 protein alone is sufficient to trigger a broad proteomic change in the skull marrow, meninges, and brain compared to the HA protein. The dysregulated proteins are enriched in pathways related to coronavirus disease, NETs formation, and neutrophil degranulation, consistent with the changes observed in virus-infected human samples.

Spike protein from the skull marrow leads to brain cortex neuronal injury
They microinjected the spike protein directly into the mice skull marrow. The spike protein reached the meninges and brain parenchyma within 30 minutes. They found brain cell death and neuronal injury 3 and 28 days after injection.

Spike protein persists in the human skull marrow
Here's the persisting bit.
They looked for spike protein in the skulls of 34 people who died from non-COVID related causes during the pandemic. They found spike protein in 10 of the people. It's inferred that these people were not testing positive to Covid-19 at the time they died.
 
From the above I am not clear that any of this explains anything relevant either to LongCovid or ME?

I am afraid that a paper with Skull-Meninges-Brain Axis in the title says to me 'We are a group of people studying brainish things who know absolutely nothing about the rest of biology and will tell you about the things we found that we wanted to find.' The skull marrow has nothing to dow with brain as far as I know. There is essentially no barrier between blood and bone marrow compartments. There is bone and dense fibrous tissue between marrow and CSF.
 
Here, we used whole mouse tissue clearing technology to visualized the spike protein distribution by S1 protein with N501Y mutation, which has been shown to infect wild-type mice through binding with mouse ACE241,42, to identify all potential tissue targets of the S1 protein and assess if S1 protein alone can induce brain pathologies in the absence of other viral proteins.
Just as aside, it's a bit sobering to read about a mutation in the Covid virus that makes it infect mice. I'm not sure if that's just a lab thing or if it is out there in wild mice. The virus must be mutating its way through a whole lot of species.

For example, several neurological symptoms have been reported, most notably the long- lasting brain fog reported by many patients and significant brain tissue loss, even in mild COVID-19 cases, which urge exploration of the mechanisms of SARS-CoV-2 induced brain damage86,87,8.
From the discussion: they talk about significant brain tissue loss in mild Covid-19 cases. I'm not sure about the strength of evidence for that.

Our data may also suggest a mechanism for the virus’s entry into the central nervous system. In both mouse and COVID-19 human tissues, we find spike protein in the SMCs, which the virus or virus components could use to travel from the skull marrow to the meninges and the brain parenchyma35–38. Of course, the virus might take other routes to reach the brain in a not mutually exclusive way.

There is essentially no barrier between blood and bone marrow compartments. There is bone and dense fibrous tissue between marrow and CSF.
Do you not find the idea of skull meninges channels connecting the skull marrow to the meninges convincing? Are the channels only vascular, so that there is still a blood brain barrier?
 
Do you not find the idea of skull meninges channels connecting the skull marrow to the meninges convincing? Are the channels only vascular, so that there is still a blood brain barrier?

I am sure there is still a blood brain barrier. Skull marrow may be close to brain but then sternal marrow is close to lung - I doubt it is of any relevance to anything. If there is viraemia - which there has to be pretty much to get the virus from your nose to everywhere else, then local routes are probably irrelevant. Virus in brain may spill out into CSF but then CSF is really just the interstitial fluid of brain (or near enough).
 
It sounds to me as though these channels aren't vascular; a very recent finding
https://news.harvard.edu/gazette/st...s-key-to-detection-of-brain-infection-injury/

Frankly I think this is just a manifestation of the way research is now done by people with little understanding of general principles of things like cell and fluid flux and inflammation. It makes absolutely no sense to suggest that there is some special traffic c between CSF and skull marrow. No doubt you can demonstrate channels and fluid or solute transit but, like the so-called discovery of brain lymphatics I don't see this as changing our understanding significantly. Everyone now is trying to make their own microfield seem important.

Why on earth would CSF 'regulate' bone marrow niches? What is 'regulate' supposed to mean here?
 
I don't consider this very compelling, this mouse model is simply too different to the human disease and I don't think the findings are relevant.
 
Press release:
Long COVID: SARS-CoV-2 spike protein accumulation linked to long-lasting brain effects

Peer-Reviewed Publication

Helmholtz Munich (Helmholtz Zentrum München Deutsches Forschungszentrum für Gesundheit und Umwelt (GmbH))

Researchers from Helmholtz Munich and Ludwig-Maximilians-Universität (LMU) have identified a mechanism that may explain the neurological symptoms of Long COVID. The study shows that the SARS-CoV-2 spike protein remains in the brain’s protective layers, the meninges, and the skull’s bone marrow for up to four years after infection. This persistent presence of the spike protein could trigger chronic inflammation in affected individuals and increase the risk of neurodegenerative diseases. The team, led by Prof. Ali Ertürk, Director at the Institute for Intelligent Biotechnologies at Helmholtz Munich, also found that mRNA COVID-19 vaccines significantly reduce the accumulation of the spike protein in the brain. However, the persistence of spike protein after infection in the skull and meninges offers a target for new therapeutic strategies.

Continues at:
https://www.eurekalert.org/news-releases/1066512

 
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