Changes in the Lipid Turnover, Composition, and Organization, as Sphingolipid-enriched Membrane Domains, in Rat Cerebellar Granule Cells Developing in Vitro

In the present paper, we report on the properties of sphingolipid-enriched domains of rat cerebellar granule cells in culture at different stages of neuronal development. The major lipid components of these domains were glycerophospholipids and cholesterol. Glycerophospholipids were 45-75% and cholesterol 15-45% of total lipids of the domains. This corresponded to 5-17% of total cell glycerophospholipids and 15-45% of total cell cholesterol. Phosphatidylcholine, mainly dipalmitoylphosphatidylcholine, was 66-85% of all the glycerophospholipids associated with these domains. Consequently, the palmitoyl residue was significantly enriched in the domains. The surface occupied by these structures increased during development. 40-70% of cell sphingolipids segregated in sphingolipid-enriched membrane domains, with the maximum ganglioside density in fully differentiated neurons. A high content of ceramide was found in the domains of aging neurons. Then, the sphingolipid/glycerophospholipid molar ratio was more than doubled during the initial stage of development, whereas the cholesterol/glycerophospholipid molar ratio gradually decreased during in vitro differentiation. Phosphorylated phosphoinositides, which were scant in the domains of undifferentiated cells, dramatically increased during differentiation and aging in culture. Proteins were minor components of the domains (0.1-2.8% of all domain components). Phosphotyrosine-containing proteins were selectively recovered in the sphingolipid-enriched domain. Among these, Src family protein-tyrosine kinases, known to participate to the process of neuronal differentiation, were associated with the sphingolipid-enriched domains in a way specific for the type of kinase and for the developmental stage of the cell. Proteins belonging to other signaling pathways, such as phosphoinositide 3-kinase and its downstream target, Akt, were not associated with the domains.