Large bone marrow cells may be responsible for COVID-19 brain fog

Large bone marrow cells may be responsible for COVID-19 brain fog
© iStock/ThitareeSarmkasat

A team of researchers has found evidence that large bone marrow cells known as megakaryocytes may be responsible for COVID-19 induced brain fog.

In severe cases of COVID-19 many patients report experiencing brain fog, known as dysexecutive syndrome, which is initially experienced whilst sick and can linger in the patient after recovery. Researchers at Johns Hopkins Medicine believe that megakaryocytes, large cells from the bone marrow that produce platelets for clotting and wound repair, are responsible for this brain fog after they discovered them within the capillaries of the brains of people who died of COVID-19.

The findings have been published as a research letter in JAMA Neurology.

Bone marrow cells

Pathologists at Johns Hopkins Medicine in Baltimore and Brigham and Women’s Hospital in Boston have suggested that megakaryocytes migrate to the brain in a journey precipitated by the destructive activity of coronavirus (SARS-CoV-2) and say that these out-of-place cells may reduce or completely block blood flow through individual capillaries in the cerebral cortex where the majority of information processing takes place.

This could lead to neurological impairment, say the researchers.

After evaluated brain tissue from autopsies of 15 patients who died of COVID-19, the team found large cell nuclei resembling those of megakaryocytes in the cortical capillaries in five of the samples, which were confirmed to be megakaryocyte immigrants from bone marrow following immunohistochemical testing. No megakaryocyte nuclei were found in post-mortem brain tissues from decedents who were negative for the COVID-19 coronavirus and served as the study’s control group.

David Nauen, MD, PhD, study lead author and assistant professor of pathology at the Johns Hopkins University School of Medicine, said: “We suspect that SARS-CoV-2 damages lung tissue, leading to the release of chemical signals that induce the megakaryocytes to travel there from the bone marrow. When that happens, these large cells somehow find a way to pass through the lung capillaries and get to the brain.

“We don’t yet know if the megakaryocytes we found in the brain are just the result of blood flow carrying them there or if a specific change occurs in the brain vessels that trap them. Because standard brain autopsy sections represent only a minute portion of the cerebral cortex, the actual numbers of these cells in the brain as a result of COVID-19 could be considerable — as could their potentially negative neurological impacts on those who survive.”

Next, the team plans to characterise what happens in the brain tissue and cortical capillaries during severe cases of COVID-19 to better understand how megakaryocytes are signalled and recruited.

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