Adaptive mutations of neuraminidase stalk truncation and deglycosylation confer enhanced pathogenicity of influenza A viruses

Sehee Park,Misun Nam,Jin-Won Song,Sun-Ho Kee,Man-Seong Park,Joon-Yong Bae,Mee Sook Park,Kirim Yoo,Jin Il Kim,Ilseob Lee,Juwon Kim,Ki-Joon Song

doi:10.1038/s41598-017-11348-0

Abstract

It has been noticed that neuraminidase (NA) stalk truncation has arisen from evolutionary adaptation of avian influenza A viruses (IAVs) from wild aquatic birds to domestic poultry. We identified this molecular alteration after the adaptation of a 2009 pandemic H1N1 virus (pH1N1) in BALB/c mice. The mouse-adapted pH1N1 lost its eight consecutive amino acids including one potential N-linked glycosite from the NA stalk region. To explore the relationship of NA stalk truncation or deglycosylation with viral pathogenicity changes, we generated NA stalk mutant viruses on the pH1N1 backbone by reverse genetics. Intriguingly, either NA stalk truncation or deglycosylation changed pH1N1 into a lethal virus to mice by resulting in extensive pathologic transformation in the mouse lungs and systemic infection affecting beyond the respiratory organs in mice. The increased pathogenicity of these NA stalk mutants was also reproduced in ferrets. In further investigation using a human-infecting H7N9 avian IAV strain, NA stalk truncation or deglycosylation enhanced the replication property and pathogenicity of H7N9 NA stalk mutant viruses in the same mouse model. Taken together, our results suggest that NA stalk truncation or deglycosylation can be the pathogenic determinants of seasonal influenza viruses associated with the evolutionary adaptation of IAVs.

Highlights

Influenza virus circulates seasonally among humans[1, 2]
The NA stalk truncation appears related with the pathogenicity increases of avian IAVs19, 20, 24, 25, 28–31, and some of these studies noted the pathogenic contribution of N-linked glycosylation (NLG) pattern changes in the globular head region of hemagglutinin (HA) protein[20, 24]
We recovered a mouse-adapted virus and identified its amino acid mutations. Of these amino acid mutations, we focused on the truncation of eight consecutive amino acids including one potential NLG site in the NA stalk region because this adaptive mutation has been reported mostly in the NAs of avian influenza A viruses (IAVs), not often in those of human seasonal strains previously

Summary

Introduction

Influenza virus circulates seasonally among humans[1, 2]. Successfully transmitting from person to person, the virus causes approximately three to five million human infections per year, which of almost 10% would be the fatal cases[3, 4]. NA stalk truncation has been suggested for its association with the adaptation of avian IAVs from wild aquatic birds to domestic poultry species[19, 20] It was reported previously in the NAs of avian influenza H2N2, H5N1, H6N1, H7N1, H7N3, and H9N2 subtype viruses[20,21,22,23,24,25,26]. We recovered a mouse-adapted (ma) virus and identified its amino acid mutations Of these amino acid mutations, we focused on the truncation of eight consecutive amino acids including one potential NLG site in the NA stalk region because this adaptive mutation has been reported mostly in the NAs of avian IAVs, not often in those of human seasonal strains previously. We explored the effects of NA stalk truncation or deglycosylation on the pathogenicity of the H7N9 human strain in mice

Methods

Results

Conclusion