α2-3-Sialylated Glycoproteins Attenuate Streptococcus mutans Virulence and Associated Host Inflammatory Responses

Glycans attached to host glycoproteins play an important role in regulating oral microbial colonization and maintaining community balance. Our previous studies revealed that children exhibit lower levels of α2-3 sialylated glycan structures (SAα2-3Gal) than adults, raising the possibility that this age-associated glycan deficiency contributes to the heightened cariogenicity of Streptococcus mutans. In this study, sialylated glycoproteins (Sia-GP) and corresponding desialylated controls (DeSia-GP and α2,3-DeSia-GP) were prepared from bovine milk-derived glycoproteins to investigate the functional contribution of SAα2-3Gal. Their effects on S. mutans were evaluated by assessing bacterial growth, acid production, biofilm formation and extracellular polysaccharide synthesis, while a human oral keratinocytes (HOK cells) infection model was used to examine epithelial cell viability, wound healing, and infection-associated inflammatory responses. The results showed that Sia-GP exerted only a transient inhibitory effect on early bacterial growth without affecting final biomass, but significantly attenuated acidogenic activity, biofilm formation, and extracellular polysaccharides production in a concentration-dependent manner. These inhibitory effects were markedly attenuated following removal of α2-3-linked sialic acids, demonstrating the essential role of SAα2-3Gal. In addition, Sia-GP alleviated S. mutans-induced cellular damage in HOK cells by improving cell viability, colony formation, and migration, while suppressing infection-associated inflammatory signaling. Collectively, these findings demonstrate that SAα2-3Gal effectively limits multiple virulence traits of S. mutans and attenuates S. mutans-induced damage in oral epithelial cells. This study provides mechanistic insights into glycan-mediated regulation of host–microbe interactions and suggests that the naturally low abundance of SAα2-3Gal in children may increase their susceptibility to S. mutans infection and caries development.