Normally, the lysosome, known as the cells’ “trash compactor,” destroys viruses before they can leave the cell. However, researchers at the National Institutes of Health (NIH) have discovered that SARS-CoV-2 is not like other viruses. The virus can deactivate that waste disposal system, exit without hindrance, and spread freely throughout the body.
“To our shock, these coronaviruses got out of the cells just fine,” said Nihal Altan-Bonnet, PhD, chief of the Laboratory of Host-Pathogen Dynamics at the National Heart, Lung, and Blood Institute, who coauthored the study report.
Most viruses exit via the biosynthetic secretory pathway, used to transport hormones, growth factors and other materials. The researchers wanted to learn whether coronaviruses took an alternate route. To find out, they conducted further studies, using microscopy and virus-specific markers. They discovered that coronaviruses somehow target the lysosome and congregate there. Although lysosomes are highly acidic, the coronaviruses were not destroyed.
That question led to more experiments. The researchers next found that lysosomes get “de-acidified” in coronavirus-infected cells, which weakens their destructive enzymes. The result: The coronavirus remains intact, ready to infect other cells upon exiting.
The coronaviruses are “very sneaky,” Altan-Bonnet says. “They’re using these lysosomes to get out, but they’re also disrupting the lysosome so it can’t do its job or function.” It’s possible that the way the coronavirus interferes with the lysosome’s “immunological machinery” underlies some of the immune system abnormalities seen in COVID-19 patients, such as cytokine storms.
Studying this coronavirus's heterodox ways may mean that researchers can figure out how to keep it from getting out unscathed, or restore the lysosome’s killing ability by re-acidifying it. Altan-Bonnet and coauthor Sourish Ghosh, PhD, say they have already identified one experimental enzyme inhibitor that potently blocks coronaviruses from exiting the cell.
The lysosome pathway, Altan-Bonnet says, “offers a whole different way of thinking about targeted therapeutics.”