Newswise – COVID-19, the disease caused by the pandemic coronavirus SARS-CoV-2, is considered primarily a respiratory infection. However, the virus has also been known to affect other parts of the body in ways that are not so well understood, sometimes with long-term consequences, such as cardiac arrhythmia, fatigue and “brain fog”. .
Researchers at the University of California, San Diego School of Medicine use stem cell-derived organoids (small balls of human cells that look and act like mini-organs in a laboratory dish) to study the interaction of the virus. with various organ systems and to develop therapies to block infection.
“We are finding that SARS-CoV-2 does not infect the whole body in the same way,” said Tariq Rana, doctor, professor and head of the Genetics Division of the Department of Pediatrics at UC San Diego School of Medicine . and the Moores Cancer Center. “In different cell types, the virus causes the expression of different genes and we see different results.”
Rana’s team published their findings on February 11, 2021 BC Stem cell reports.
Like many organs, the team’s lung and brain organoids produce the ACE2 and TMPRSS2 molecules, which settle like door knobs on the outer surfaces of cells. SARS-CoV-2 grabs these knobs from the door with its spike protein as a means to enter cells and establish infection.
Rana and the team developed a pseudovirus, a non-infectious version of SARS-CoV-2, and labeled it with green fluorescent protein or GFP, a bright molecule derived from jellyfish that helps researchers visualize the inner workings of cells. · Cells. Fluorescent labeling allowed them to quantify the binding of the virus ear protein to ACE2 receptors on human lung and brain organoids and to evaluate cell responses.
The team was surprised to see approximately 10 times more ACE2 and TMPRSS2 receptors and therefore a much higher viral infection in lung organoids, compared to brain organoids. Treatment with spike viral protein or TMPRSS2 inhibitors reduced infection levels in both organoids.
“We saw fluorescence spots on the brain organoids, but it was the lung organoids that really lit up,” Rana said.
In addition to differences in levels of infectivity, lung and brain organoids also differ in their responses to the virus. SARS-CoV-2-infected lung organoids bombarded molecules intended to call for help from the immune system: interferons, cytokines, and chemokines. Infected brain organoids, on the other hand, increased the production of other molecules, such as TLR3, a member of the toll-like receptor family that plays a key role in pathogen recognition and innate immunity activation.
Rana explained that while at first it might seem that the organoid reaction of the brain is just another form of immune response, these molecules can also help with programmed cell death. Rana’s team previously saw a similar response of brain cells to the Zika virus, an infection known to slow neonatal brain development.
“The way we see brain cells react to the virus may help explain some of the neurological effects reported by patients with COVID-19,” Rana said.
Of course, organoids are not exact replicas of human organs. They lack blood vessels and immune cells, for example. But they provide an important tool for studying diseases and testing potential therapies. According to Rana, organoids mimic the real-world human condition more accurately than cell lines or animal models that have been designed to overexpress human ACE2 and TMPRSS2.
“In animals that overexpress ACE2 receptors, you see that everything lights up with the infection, even the brain, so everyone thinks that’s the real situation,” Rana said. “But we’ve found that’s probably not the case.”
In addition to its work with the pseudovirus, the team validated its findings by applying SARS-CoV-2 infecting live to lung and brain organoids in a biosafety-3-level laboratory, a facility specially designed and certified to study safely high-risk microbes. .
Now, Rana and his collaborators are developing SARS-CoV-2 inhibitors and testing their functioning in organoid models derived from people of different ethnic and racial backgrounds representing the diverse population of California. They have recently received new funding from the California Institute of Regenerative Medicine to support the work.
Co-authors of the study include: Shashi Kant Tiwari, Shaobo Wang, Davey Smith and Aaron Carlin, all at UC San Diego.
Funding for this research came, in part, from the National Institutes of Health (grants CA177322, DA039562, DA049524, and AI125103), Burroughs Wellcome Fund, and John and Mary Tu Foundation.
Disclosure: Tariq Rana is the founder of ViRx Pharmaceuticals and has a stake in the company. The terms of this agreement have been reviewed and approved by the University of California at San Diego in accordance with its conflict of interest policies.