Cell surface sphingolipid glycohydrolases in neuronal differentiation and aging in culture.

Qualitative and quantitative changes in glycosphingolipids, together with changes in the expression of the corresponding glycosyltransferases, have been reported along neuronal differentiation and aging. Plasma membrane (PM) glycosphingolipid pattern and content are the result of a complex network of metabolic pathways, including those potentially involving the activity of PM glycohydrolases. We analyzed the total cell activities of sialyltransferase I, II and IV, sialidase, β-galactosidase and β-glucosidase, and the PM-associated activities of sialidase Neu3, β-galactosidase, Conduritol B Epoxide-sensitive β-glucosidase and β-glucosidase GBA2 in rat cerebellar granule cells along differentiation and aging in culture. Sialyltransferase activities increased during cell differentiation, in agreement with the known increase of the total ganglioside content during neuronal maturation. The remodeling of ganglioside pattern could be because of the augmented activities of total sialidase and, within PM, to the action of the cell surface associated sialidase Neu3. Sialidase activities remained high during aging, in agreement with the known progressive ganglioside reduction in brain senescence. As PM β-galactosidase and β-glucosidase activities and parallely ceramide levels markedly increased along in vitro aging, PM ceramide production in neurons might be because of local catabolism of glycosphingolipids and not only to that of sphingomyelin, as already reported in human fibroblasts.