The Modern Equine Vet
January 2024
Vol 14 Issue 1 2024
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Infectious Disease

How Eastern Equine Encephalitis Virus Invades Brain Cells

By Tamara Schneider

It may be possible to set up a decoy and prevent eastern equine encephalitis (EEE) from entering the brain.

Scientists predict that as the planet warms and lengthens the mosquito populations’ seasons and geographical reach, risk of infection will grow among horses and humans.

Co-senior authors Michael S. Diamond, MD, PhD, the Herbert S. Gasser Professor at Washington University. and Daved H. Fremont, PhD, a professor of pathology & immunology, investigated how the virus attaches to 1 of its key receptors—very low-density lipoprotein receptor (VLDLR), which is found on the surface of cells in the brain and other parts of the body.

Co-first author Lucas Adams, an MD/PhD student in the Fremont and Diamond laboratories, used cryo-electron microscopy to reconstruct the virus binding to the receptor in atomic-level detail. The results turned out to be unexpectedly complex. The molecule is composed of 8 repeated segments, called domains, strung together like beads on a chain. Usually, a viral protein and its receptor fit together in one very specific way. In this case, however, 2 or 3 different spots on the viral surface proteins could attach to any of 5 of the molecule’s 8 domains.

“What’s really striking is that we find multiple binding sites, but the chemistry of each of the binding sites is similar and also similar to the chemistry of binding sites for other viruses that interact with related receptors,” said Dr. Fremont, who is also a professor of biochemistry & molecular biophysics and of molecular microbiology. “The chemistry just works out well for the way viruses want to attach to cell membranes.”
The domains that make up this molecule also are found in several related cell-surface proteins. Similar domains are found in proteins from across the animal kingdom.

“Since they’re using a molecule that naturally has repetitive domains, some of the alphaviruses have evolved to use the same strategy of attachment with multiple different domains in the same receptor,” said Dr. Diamond, who is also a professor of medicine, of molecular microbiology, and of pathology & immunology. Alphaviruses include EEE virus and several others that cause brain or joint disease. “There are sequence differences in the VLDLR receptor over evolution in different species, but since the virus has this flexibility in binding, it is able to infect a wide variety of species including mosquitoes, birds, rodents and humans.”

To block attachment, the researchers created a panel of decoy receptors by combining subsets of the 8 domains. The idea was that the virus mistakenly would bind to the decoy instead of the receptor on cells, and the decoy with the virus attached could then be cleared away by immune cells.

Co-first author Saravanan Raju, MD, PhD, a postdoctoral researcher in the Diamond lab, evaluated the panel of decoys. First, he tested them on cells in vitro; many neutralized the virus. Then, he turned to mice. Dr. Raju pretreated mice with a decoy or saline solution, as a control, 6 hours before injecting the virus under their skin, a mode of infection that mimics natural infection via mosquito bite. Three decoys were tested: 1 known to be unable to neutralize the virus; 1 made from the full-length molecule; and 1 made from just the first 2 domains.

All the mice that received saline solution, the non-neutralizing decoy or the full-length decoy died within eight days of infection. All the mice that received the decoy made from the first two domains survived without signs of illness.

Certain aspects of its biology give Eastern equine encephalitis virus the potential to be weaponized, making it particularly important to find a way to protect against it. In a subsequent experiment in which the mice were infected by inhalation, the decoy made from the first 2 domains was still effective, reducing the mice’s chance of death by 70%.

“Through a combination of the structural work and the domain deletion work, we were able to figure out which domains are the most critical and create a quite effective decoy receptor that can neutralize viral infection,” Dr. Fremont said.

Researchers at Washington University School of Medicine in St. Louis said their findings should advance the understanding of the complex molecular interactions between viral proteins and their receptors on animal cells. The findings lay a foundation for treatments and vaccines for viral infections.

“Understanding how viruses engage with the cells they infect is a critical part of preventing and treating viral disease,” Dr. Diamond said. “Once you understand that, you have the foundation for developing vaccines and drugs to block it. In this study, it took us a long time to sort out the complexity associated with the particular receptor-virus interaction, but once we acquired this knowledge, we were able to design a decoy molecule that turned out to be very effective at neutralizing the virus and protecting mice from disease.” MeV

The story was original published on the Washington University website. It has been edited for style. https://medicine.wustl.edu/news/study-reveals-new-clues-to-how-eastern-equine-encephalitis-virus-invades-brain-cells/

For more information:
Adams LJ, Raju S, Ma H, et al. Structural and functional basis of VLDLR usage by eastern equine encephalitis virus. Cell. 2024 Jan 3; doi: 10.1016/j.cell.2023.11.031 https://dx.doi.org/10.1016/j.cell.2023.11.031

 

EEE virus attaches to a receptor it uses to enter and infect cells. The whole virus is shown on the left and a magnified view of the viral structural proteins on the right. The findings lay the groundwork for a receptor decoy molecule that protects mice from encephalitis caused by the virus.
Images by Lucas Adams