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Metabolic Glycoengineering with Azide- and Alkene-Modified Hexosamines: Quantification of Sialic Acid Levels.

ABSTRACT: Metabolic glycoengineering (MGE) is an established method to incorporate chemical reporter groups into cellular glycans for subsequent bioorthogonal labeling. The method has found broad application for the visualization and isolation of glycans allowing their biological roles to be probed. Furthermore, targeting of drugs to cancer cells that present high concentrations of sialic acids on their surface is an attractive approach. We report the application of a labeling reaction using 1,2-diamino-4,5-methylenedioxybenzene for the quantification of sialic acid derivates after MGE with various azide- and alkene-modified ManNAc, GlcNAc, and GalNAc derivatives. We followed the time course of sialic acid production and were able to detect sialic acids modified with the chemical reporter group - not only after addition of ManNAc derivatives to the cell culture. A cyclopropane-modified ManNAc derivative, being a model for the corresponding cyclopropene analog, which undergoes fast inverse-electron-demand Diels-Alder reactions with 1,2,4,5-tetrazines, resulted in the highest incorporation efficiency. Furthermore, we investigated whether feeding the cells with natural and unnatural ManNAc derivative results in increased levels of sialic acids and found that this is strongly dependent on the investigated cell type and cell fraction. For HEK 293T cells, a strong increase in free sialic acids in the cell interior was found, whereas cell-surface sialic acid levels are only moderately increased.

SUBMITTER: Dold JEGA

PROVIDER: S-EPMC8048827 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The glycocalyx-a plethora of sugars forming a dense layer that covers the cell membrane-is commonly found on the epithelial surface of lumen forming tissue. New glycocalyx specific properties have been defined for various organs in the last decade. However, in the lung alveolar epithelium, its structure and functions remain almost completely unexplored. This is partly due to the lack of physiologically relevant, cost effective in vitro models. As the glycocalyx is an essential but neglected part of the alveolar epithelial barrier, understanding its properties holds the promise to enhance the pulmonary administration of drugs and delivery of nanoparticles. Here, using air-liquid-interface (ALI) cell culture, we focus on combining metabolic glycoengineering with glycan specific electron and confocal microscopy to visualize the glycocalyx of a recently immortalized human alveolar epithelial cell line (hAELVi). For this purpose, we applied different bioorthogonal labeling approaches to visualize sialic acid-an amino sugar that provides negative charge to the lung epithelial glycocalyx-using both fluorescence and gold-nanoparticle labeling. Further, we compared mild chemical fixing/freeze substitution and standard cytochemical electron microscopy embedding protocols for their capacity of contrasting the glycocalyx. In our study, we established hAELVi cells as a convenient model for investigating human alveolar epithelial glycocalyx. Transmission electron microscopy revealed hAELVi cells to develop ultrastructural features reminiscent of alveolar epithelial type II cells (ATII). Further, we visualized extracellular uni- and multilamellar membranous structures in direct proximity to the glycocalyx at ultrastructural level, indicating putative interactions. The lamellar membranes were able to form structures of higher organization, and we report sialic acid to be present within those. In conclusion, combining metabolite specific glycoengineering with ultrastructural localization presents an innovative method with high potential to depict the molecular distribution of individual components of the alveolar epithelial glycocalyx and its interaction partners.

Dataset Information

Metabolic Glycoengineering with Azide- and Alkene-Modified Hexosamines: Quantification of Sialic Acid Levels.

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