Cell Surface Sialylated N-Glycan Alterations during Development

Abstract

This brief survey focuses on the comparison of sialylated N-glycans of embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), mesenchymal stem cells (MSCs) and of differentiated cells. In addition, the impact of sialic acid (Sia) deficiency on cell surfaces during development is summarized. The most common Sia is N-acetylneuraminic acid (Neu5Ac). The branched structures of complex-and hybrid-type N-glycans are the carrier for Sia. Transmembrane adhesive proteins, voltage-gated ion channels and many ligand-activated receptors are some examples of heavily sialylated N-glycan bearing membrane proteins. Their oligosaccharide extensions provide an important contribution to glycocalyx glycans. ESCs and iPSCs are characterized with high mannose-type and biantennary complex-type core structures. Two branches terminate with α2,6-linked Sia. MSCs contain high mannose, hybrid-and complex-type N-glycans. Linear poly-N-acetyllactosamine (poly-Galβ1-4GlcNAc, poly-LacNAc) chains are the characteristic structures. Both α2,3-and α2,6-linked Sias are seen in a species-specific manner in MSCs. α2,6-linked Sia is probably a marker associated with the multipotency of human MSCs. Differentiated healthy cells contain the most abundant 2-branched complex structures. The bisecting branch on the core structure appears as a differentiation marker. poly-LacNAc chains are terminated with α2,3-and α2,6-linked Sia, with the former being higher. poly-LacNAc sequences have a high affinity for β-galactoside recognizing lectin and galectin. Galectin forms a lattice structure with the N-glycans of glycoproteins anchored to the plasma membrane. The impact of N-glycangalectin complexes in cell biology is summarized. Finally, the effect of reduced Sia on clearance of aged cells is explained. Experimental evidence for the masking role of Sia in the regulation of histolysis in aged cells is revealed.