Thanks to the dedication, hard work and lost hours of sleep by millions of scientists around the world, we now know enough about COVID-19 and SARS-CoV-2 to at least battle back the virus with vaccines. However, COVID-19 hasn’t played a prominent enough role in our lives long enough for anyone to define the long-term effects—some of which we’ve already begun seeing.
Deemed COVID-19 “long-haulers,” there is a subsect of survivors who continue to experience symptoms such as shortness of breath, dizziness and cognitive impairment many months after clearing the infection.
In research not yet published but presented Friday at the Experimental Biology 2021 meeting, researcher Nicholas Evans and his team unveiled clues as to the types of biological processes that affect—and persist—in human cells and genes post-COVID-19 infection.
Evans, a master’s student at Texas Tech University Health Sciences Center, focused his work on the direct impact of SARS-CoV-2 spike proteins on airway cells.
"We found that exposure to the SARS-CoV-2 spike protein alone was enough to change baseline gene expression in airway cells," said Evans. "This suggests that symptoms seen in patients may initially result from the spike protein interacting with the cells directly."
For their study, the researchers first had to optimize the air liquid interface cell culture technique to simulate the physiological conditions in the lung airway in vitro. This involved exposing cells to air, then giving them time to mature into airway cells. Once established, the team grew human primary bronchial epithelial cells (HBECs) before exposing them to a low (50 ng/mL) or high (5 ug/mL) concentration of recombinant SARS-CoV-2 spike protein.
The researchers then screened 84 genes related to different pathways to stress.
“We used this to see where the spike protein is causing changes and see which pathway is most affected so that we could further explore the genes there,” Evans explained during his presentation.
The team found that over- and under-expressed genes were related to oxidative stress, hypoxia signaling and osmotic stress. However, it was inflammatory response that had the most genes overexpressed—three—and the most significant p values and greater fold regulation. Specially, genes CCL2, IL1A and IL1B showed extensive fold changes in both the low and high concentration treatments that remained even after the cells recovered from exposure.
"Our work helps to elucidate changes occurring in patients on the genetic level, which could eventually provide insight into which treatments would work best for specific patients," said Evans.
Using cells collected from COVID-19 patients, the researchers confirmed their new air liquid interface cell culture approach does indeed accurately reflect what occurs in the human body during SARS-CoV-2 infection.
“[This demonstrates] the spike protein alone can be used to student the molecular mechanisms underlying SARS interactions with airway epithelial cells,” said Evans. “This enables more labs without BSL3 facilities to study SARS.”
Continuing their research, Evans and his team are now screening air liquid interface cultures with longer intervals—from 48 hours up to 6 months—to investigate the persistence of human immune responses.
Photo: Nicholas Evans changes the growth media in the Transwell plate that is used to grow and differentiate airway cells. Credit: Nicholas Evans/Texas Tech University Health Sciences Center