Serum glycomarkers of endoplasmic reticulum and lysosomal-endosomal system stress in human healthy aging and diseases.

To verify the idea that extracellular free oligosaccharides might be able to reflect the functional status of the endoplasmic reticulum (ER) and lysosomal-endosomal system, HPLC-profiles of serum-derived free oligosaccharides (FOS) in human healthy aging, acute myeloproliferative neoplasms, and cardiovascular pathologies were compared with intracellular glycans. After plasma deproteinization and FOS purification the oligosaccharides were labelled with anthranilic acid, separated into the neutral and charged with QAE Sephadex (Q25-120) chromatography and analysed using high-performance liquid chromatography (HPLC). The charged FOS were digested with a sialidase and compared with free oligosaccharides from transferrin for structural decoding.

"Three sources and three component parts" of free oligosaccharides.

Metabolism of glycoproteins and glycolipids is accompanied by the appearance of unbound structural analogues of the carbohydrate portion of glycoconjugates or so called free oligosaccharides. There are their several sources inside the cell: 1) multistep pathways of N-glycosylation, 2) the cell quality control and ER-associated degradation of misglycosylated and/or misfolded glycoproteins, 3) lysosomal degradation of mature glycoconjugates. In this review the information about the ways of free oligosaccharides appearance in different cell compartments and details of their structures depending on the source is summarized.