Norovirus RNA folding regulates its life cycle, opening a path to attenuated vaccines

A study has found that norovirus RNA is not merely a carrier of genetic information but also regulates the virus’s life cycle through its three-dimensional folded structure. The researchers said this structure could be used to design genetically stable, infectious attenuated vaccines.

According to the international journal Cell on the 19th (local time), a team led by Anna Marie Pyle, a professor at Yale University, reported results from a study that directly measured the structure of mouse norovirus (MNV) genomic RNA inside infected cells.

Norovirus is a leading cause of acute gastroenteritis worldwide, infecting about 685 million people and causing 200,000 deaths each year. However, vaccine and antiviral development for human norovirus has been slow because large-scale cell culture systems and animal models are lacking.

The team analyzed the secondary structure of the entire 7.4-kb MNV genomic RNA using two in-cell chemical probing techniques, SHAPE-MaP and fbDMS-MaP. The analysis identified numerous highly structured RNA elements that are evolutionarily conserved across the genus Norovirus.

The researchers designed antisense locked nucleic acids (LNAs) targeting specific structural elements and significantly inhibited viral replication. They also created “structure-disrupting mutants” that altered only the RNA structure through point mutations while leaving the coding sequence unchanged.

These mutants showed lower viral RNA levels in wild-type mice and attenuated characteristics, including reduced weight loss and mortality, in immunodeficient mice. Luciferase experiments also confirmed that specific structural elements regulate viral translation in a structure-dependent manner.

The team said the structure-disrupting mutants were genetically stable, with no reversion mutations during serial cell culture, and induced a protective immune response upon secondary infection while limiting viral replication.

Because the study was validated in a mouse model, the potential to extend the findings to human norovirus requires further testing. The mutants’ safety and immunogenicity in humans, as well as delivery and cost issues for LNAs, also remain challenges for clinical application.

“This study showed that RNA structure plays a central role in norovirus biology and presented a general framework for designing RNA structure-based antiviral vaccines and therapeutics,” the team said. The researchers said the approach could also be used to develop vaccines for other RNA viruses, including coronaviruses and flaviviruses.