SARS-CoV-2 spike protein found to remain in brain regions

New research reveals just how long spike protein Research at the brain border could explain the neurological symptoms of long-term coronavirus infection and highlight the protective role of vaccines.

study: Retention of spike protein in the skull-meninges-brain axis may contribute to neurological sequelae of COVID-19 infection. Image credit: sciencepics / Shutterstock

In a recent study published in the journal Cell Host & Microbe, researchers investigated the persistence of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) spike protein in the cranium-meninges-brain axis and We investigated its role in neurological sequelae associated with coronavirus. Disease of 2019 (COVID-19).

background

SARS-CoV-2 infection, even in mild cases, is associated with a variety of neurological complications, including brain fog, decreased gray matter thickness, and increased risk of stroke. Although viral ribonucleic acid (RNA) is not consistently detected in brain tissue, widespread immune activation is observed, suggesting an indirect mechanism.

The SARS-CoV-2 spike protein is one of the key structural components of the virus, triggering an inflammatory response through Toll-like receptors, affecting endothelial function, and forming proinflammatory blood clots.

Recent evidence suggests that it persists in immune cells and plasma for long periods of time, prompting further research. Understanding its distribution and functional impact on the brain and other organs could shed light on both the acute and chronic neurological sequelae of COVID-19 infection.

About research

SARS-CoV-2 omicron and SARS-CoV-2 green fluorescent protein (GFP)-tagged virus strains were prepared and utilized for mouse infection studies. Transgenic K18 human angiotensin-converting enzyme 2 (K18-hACE2) mice and wild-type C57BL/6J mice were aerosol inoculated with specific virus titers to assess the impact of the virus. The immunization protocol included intramuscular administration of BNT162b2 messenger RNA (mRNA) vaccine prior to virus exposure. Infected mice were observed for clinical symptoms, weighed daily, and euthanized at designated time points.

This study also included injections of fluorescently labeled recombinant Spike S1 protein to assess systemic and local effects.

During the intravenous and craniomedullary microinjection procedure, anesthesia was induced and the injection targeted both the peripheral tissues and the cancellous bone marrow of the skull. After injection, tissue perfusion was performed using phosphate-buffered saline (PBS) and paraformaldehyde (PFA) to achieve fixation for subsequent analysis. Tissue removal with the Solvent Depleted Organ Three-Dimensional Imaging (3DISCO) protocol rendered mouse tissue optically clear, facilitating detailed imaging of viral protein distribution with advanced microscopy.

High-resolution imaging techniques such as confocal microscopy have made it possible to precisely visualize the tissues of the human brain and skull. Immunofluorescence, laser capture microdissection, and mass spectrometry provided insight into proteomic changes and inflammatory pathways associated with spike protein persistence.

Behavioral assessments, ischemia models, and traumatic brain injury (TBI) experiments evaluated the functional consequences of spike protein persistence in the brain and peripheral tissues. Comprehensive statistical analysis validated the results and ensured accurate interpretation of the data.

Research results

Study reveals persistent presence of SARS-CoV-2 spike protein in skulls, meninges, and brains of COVID-19 patients, highlighting potential neurological effects of the virus .

Researchers used advanced tissue removal and imaging techniques to detect spikes from the cranial spinal cord, the recently discovered cranial meningeal junction (SMC), and the meninges of patients who died from acute COVID-19 infection. Protein was detected. In the cranial marrow, 45% of the spike protein was found outside the blood vessels, suggesting extravasation into the tissue.

Additionally, 27% of the spike protein colocalized with ionized calcium-binding adapter molecule 1 (Iba1)-positive myeloid cells. Spike protein was also detected in the perinuclear space of meningeal cells and near NeuN-positive neurons in the frontal cortex of the brain, indicating an interaction with neuronal areas.

Interestingly, while SARS-CoV-2 RNA is often undetectable in brain samples, the spike protein persists, suggesting a long half-life or a unique uptake mechanism distinct from active viral replication. has been. In non-COVID-19 deaths, the spike protein remains in craniomedullary samples long after infection, and is associated with tau protein in cerebrospinal fluid (CSF), neurofilament light chain (NfL), and is correlated with increased levels of glial fibrillary acidic protein (GFAP). COVID-19 infectious patients. These markers indicate ongoing neurodegeneration and support the hypothesis that spike proteins contribute to chronic neurological symptoms.

These findings were confirmed in a mouse model, where SARS-CoV-2 infection resulted in the distribution of the spike protein throughout various organs, including the cranial marrow and cerebral cortex, even after viral RNA was reduced. The spike protein was also shown to cross the blood-brain barrier (BBB) ​​and localize to ACE2-expressing tissues.

Proteomic analysis revealed significant changes in craniomedullary, meningeal, and cerebral cortical tissues, including neutrophil extracellular traps (NETs), mitogen-activated protein kinases (MAPKs), and phosphoinositide 3-kinase (PI3K)-proteins. Pathways such as kinase B (AKT) have been implicated. On cue. These changes are particularly pronounced in certain regions of the spike protein and contribute to lysosomal activation, axonal damage, and neurodegeneration-related markers.

Functional studies confirmed the pathological effects of the spike protein. Microinjection into the craniomedullary gland caused neuroinflammation, neuronal damage, and lysosomal activation. Behavioral experiments reveal spike protein-induced anxiety-like behavior in mice and worsening traumatic brain injury and stroke outcomes leading to increased long-term brain damage.

Finally, the mRNA vaccine reduced, but did not completely eliminate, spike protein accumulation in mice, particularly in the brain and skull regions.

conclusion

In summary, the long-term neurological effects of COVID-19 infection, such as brain fog and tissue loss, are associated with persistent spike protein, systemic symptoms. inflammationBBB confusion. The spike protein was also detected in postmortem samples of the patients' skulls, meninges, and brains that were negative for polymerase chain reaction (PCR), suggesting that the protein was present for a long time. Studies in mice revealed that spike protein accumulates in the cranial bone marrow and SMCs, inducing inflammation, anxiety-like behavior, and worse outcomes in brain injury models.

Advanced proteomic analyzes have revealed common markers with neurodegenerative diseases such as Alzheimer's disease, highlighting overlap with chronic neurological diseases. Vaccination reduced spike protein levels and associated inflammation, highlighting its role in mitigating both acute and chronic effects.