Resident microbes shape the vaginal epithelial glycan landscape

Abstract

Epithelial cells are covered in carbohydrates. This glycan coat or glycocalyx interfaces directly with microbes, providing a protective barrier against potential pathogens. Bacterial vaginosis is a condition associated with adverse health outcomes in which bacteria reside in direct proximity to the vaginal epithelium. Some of these bacteria, including Gardnerella, produce glycosyl hydrolase enzymes. However, glycans of the vaginal epithelial surface have not been studied in detail. Here we elucidate key characteristics of the vaginal epithelial glycan landscape and determine the impact of resident microbes on the surface glycocalyx. In BV, the glycocalyx was visibly diminished. We show that the normal vaginal epithelium displays sialylated N- and O-glycans by biochemical and mass spectrometric analysis. In contrast, BV-epithelial cell glycans were strikingly depleted of sialic acids, with underlying galactose residues exposed on the surface. Treatment of cells from BV-negative women with recombinant Gardnerella sialidases generated BV-like glycan characteristics. Together these data provide the first evidence that the vaginal epithelial glycocalyx is attacked by hydrolytic enzymes in BV. Given the widespread structural and functional roles of sialoglycans in biology and disease, these findings may point to a shared epithelial pathophysiology underlying the many adverse outcomes associated with BV.

Mucus production, host-microbiome interactions, hormone sensitivity, and innate immune responses modeled in human cervix chips

“…5g,h ). Importantly, similar changes in sialylated O-glycans have been previously observed in BV-associated mucus in vivo 30,90 . The loss of sialic acids in the mucus may reduce interactions between mucin molecules and contribute to the changes in the physical properties of mucus (e.g., lower viscosity, decreased fern branching) that we observed in the Cervix Chip.…”

Prevotella timonensisdegrades the vaginal epithelial glycocalyx through high fucosidase and sialidase activities

“…The removal of sialic acids renders mucins more vulnerable to further degradation by glycosyl hydrolases and proteases ( 63 ). A recent paper showed that recombinant sialidases of Gardnerella species led to desialylation of glycans in VK2/E6E7 and induced pathways of cell death, differentiation, and inflammatory responses ( 64 ). Therefore, these enzymes are important virulence factors that can contribute to the establishment and development of BV.…”

“…Based on these combined observations, we propose that P. timonensis may be an initial colonizer of the vaginal epithelium and does not require an established G. vaginalis biofilm. After attachment, the high sialidase and fucosidase activity of P. timonensis at the vaginal epithelial surface removes the protective terminal glycans of the glycocalyx likely creating new binding sites for secondary colonizers ( 64 , 75 ) and enhancing bacterial colonization of the upper parts of the FRT ( 76 ).…”

Prevotellaare major contributors of sialidases in the human vaginal microbiome

“…Though we did not observe inhibition of GvNanH3 by Zanamivir in our experimental setup, it is possible that this enzyme can be partially inhibited as was previously demonstrated 31 . In an accompanying paper substrates such as human vaginal epithelial cell surface glycans 33 , glycan arrays 34 , or in more complex or natural settings 35,18 .…”

“…It is possible that Gv NanH4 acts intracellularly on an as-yet-uncharacterized substrate given its lack of a signal peptide, or is inactive, similar to the Group B Streptococcus sialidase NonA 28 . Future work should examine sialidase activity towards additional substrates such as human vaginal epithelial cell surface glycans 33 , glycan arrays 34 , or in more complex or natural settings 35,18 .…”