A Brazilian study published in the journal PNAS describes some of the effects infection by SARS-CoV-2 can have on the central nervous system. A preliminary version (not yet peer-reviewed) posted in 2020 was one of the first to show that the virus that causes COVID-19 can infect brain cells, especially astrocytes. It also broke new ground by describing alterations in the structure of the cortex, the most neuron-rich brain region, even in cases of mild COVID-19.
The cerebral cortex is the outer layer of gray matter over the hemispheres. It is the largest site of neural integration in the central nervous system and plays a key role in complex functions such as memory, attention, consciousness, and language.
The investigation was conducted by several groups at the State University of Campinas (UNICAMP) and the University of São Paulo (USP), all funded by FAPESP. Researchers at the Brazilian Biosciences National Laboratory (LNBio), D’Or Institute (IDOR) and the Federal University of Rio de Janeiro (UFRJ) also contributed to the study.
“Two previous studies detected the presence of the novel coronavirus in the brain, but no one knew for sure if it was in the bloodstream, endothelial cells [lining the blood vessels] or nerve cells. We showed for the first time that it does indeed infect and replicate in astrocytes, and that this can reduce neuron viability,” Daniel Martins-de-Souza, one of the leaders of the study, told Agência FAPESP. Martins-de-Souza is a professor at UNICAMP’s Biology Institute and a researcher affiliated with IDOR.
Astrocytes are the most abundant central nervous system cells. Their functions include providing biochemical support and nutrients for neurons; regulating levels of neurotransmitters and other substances that may interfere with neuronal functioning, such as potassium; maintaining the blood-brain barrier that protects the brain from pathogens and toxins; and helping to maintain brain homeostasis.
Infection of astrocytes was confirmed by experiments using brain tissue from 26 patients who died of COVID-19. The tissue samples were collected during autopsies conducted using minimally invasive procedures by Alexandre Fabro, a pathologist and professor at the University of São Paulo’s Ribeirão Preto Medical School (FMRP-USP). The analysis was coordinated by Thiago Cunha, also a professor in FMRP-USP and a member of the Center for Research on Inflammatory Diseases (CRID).
