Differential expression of sialic acid on porcine organs during the maturation process

Sialylated structures play important roles in cell communication, and change in a regulated manner during development and differentiation. In this work, we report the main glycosidic modifications that occur during the maturation of porcine tissues, involving the sialylation process as determined with lectins. Sialic acids were identified at several levels in a broad range of cell types of nervous, respiratory, genitourinary and lymphoid origin. Nevertheless, the most contrasting was the type of glycosidic linkage between 5-N-acetyl-neuraminic acid (Neu5Ac) and galactose (Gal) expressed in central nervous system (CNS). Newborn CNS abundantly expressed Neu5Acalpha2,3Gal, but weakly or scarcely expressed Neu5Acalpha2,6Gal/GalNAc. Maturation of CNS induced drastic changes in sialic acid expression. These changes include decrease or complete loss of NeuAcalpha2,3Gal residues, mainly in olfactory structures and brain cortex, which were replaced by their isomers Neu5Acalpha2,6Gal/GalNAc. In the brain cortex and cerebellum, the increase of Neu5Acalpha2,6Gal/GalNAc molecules was paralleled by an increase of 5-N-acetyl-9-O-acetyl-neuraminic acid (Neu5,9Ac2). In addition, terminal Gal and N-acetyl-D-galactosamine (GalNAc) residues also increased their expression in adult CNS tissues, but this was more significant in structures forming the encephalic trunk. Our results show that sialylation of porcine CNS is finely modulated throughout the maturation process.