The effects of modified sialic acids on mucus and erythrocytes on influenza A virus HA and NA functions

Abstract

25Sialic acids (Sia) are the primary receptors for influenza viruses, and are widely displayed on cell surfaces and in secreted mucus. Sia may be present in variant forms that include O-acetyl modifications at C4, C7, C8, and C9 positions, and N-acetyl or N-glycolyl at C5. They can also vary in their linkages, including α2-3 or α2-6-linkages. Here, we analyzed the distribution of modified Sia in cells and tissues of wild-type mice, or in mice lacking cytidine 5'-30 monophosphate-N-acetylneuraminic acid hydroxylase (CMAH) enzyme that synthesizes Nglycolyl modifications (Neu5Gc). We also examined the variation of Sia forms on erythrocytes and saliva from different animals. To determine the effect of Sia modifications on influenza A virus (IAV) infection, we tested for effects on hemagglutinin (HA) binding and neuraminidase (NA) cleavage. We confirmed that 9-O-acetyl, 7,9-O-acetyl, 4-O-acetyl, and Neu5Gc 35 modifications are widely but variably expressed in mouse tissues, with the highest levels detected in the respiratory and gastrointestinal tracts. Secreted mucins in saliva and surface proteins of erythrocytes showed a great degree of variability in display of modified Sia between different species. IAV HA from different virus strains showed consistently reduced binding to both Neu5Gc and O-acetyl modified Sia; however, while IAV NA were inhibited by Neu5Gc and 40 O-acetyl modifications, there was significant variability between NA types. The modifications of Sia in mucus may therefore have potent effects on the functions of IAV, and may affect both pathogens and the normal flora of different mucosal sites. (241 words) IMPORTANCE 45Sialic acids (Sia) are involved in many different cellular functions and are receptors for many pathogens. Sia come in many chemically modified forms but we lack a clear understanding of how they alter the interactions with microbes. Here we examine the expression of modified Sia in mouse tissues, on secreted mucus in saliva, and on erythrocytes, including those from IAV host species and animals used in IAV research. These Sia forms varied considerably between

Sequence dynamics of three influenza A virus strains grown in different MDCK cell lines, including those expressing different sialic acid receptors

“…Neu5Gc modifications to Sia have previously been found to inhibit IAV HA binding and NA cleavage efficiency (Barnard et al., 2020; Broszeit et al., 2019). In addition to the single viral population passaged ten times in MDCK‐CMAH, an additional replicate of five passages in three separate virus populations were performed to compare SNVs that arose after MDCK‐CMAH versus MDCK‐WT passage to determine if there were differences in number and location of SNVs in HA or NA (Figure 2).…”

Sialic acid O-acetylation: From biosynthesis to roles in health and disease

“…For more detailed information on the sialic acid-virus interplay we refer to these recent reviews (19,(212)(213)(214)(215). Human Influenza A and B virus (IAV, IBV) that cause the seasonal flu express hemagglutinin (HA) and sialidase (neuraminidase, NA) glycoproteins for binding to and release from non-acetylated sialic acids, respectively, with preference for α2-6-linked sialic acids displayed on N-glycans (3,216,217). In contrast to IAV and IBV, influenza C (ICV) and D (IDV) viruses display only one multifunctional hemagglutinin esterase fusion (HEF) glycoprotein on their surface which mediates binding to Neu5,9Ac 2 (and Neu5Gc9Ac), uptake into host cells, and deacetylation during release of progeny virus (88,(218)(219)(220)(221) (Figure 3B).…”