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 n euronal development. The major lipid components of these domains were glyce rophospholipids and cholesterol, Glycerophospholipids were 45-75% and chole sterol 15-45% of total lipids of the domains. This corresponded to 5-17% of total cell glycerophospholipids and 15-45% of total cell cholesterol, Phos phatidylcholine, mainly dipalmitoylphosphatidylcholine, was 66-85% of all t he glycerophospholipids associated with these domains. Consequently, the pa lmitoyl residue was significantly enriched in the domains. The surface occu pied by these structures increased during development. 40-70% of cell sphin golipids segregated in sphingolipid-enriched membrane domains, with the max imum 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 s tage of development, whereas the cholesterol/glycerophospholipid molar rati o gradually decreased during in vitro differentiation. Phosphorylated phosp hoinositides, which were scant in the domains of undifferentiated cells, dr amatically increased during differentiation and aging in culture. Proteins were minor components of the domains (0.1-2.8% of all domain components). P hosphotyrosine-containing proteins were selectively recovered in the sphing olipid-enriched domain. Among these, Src family protein-tyrosine kinases, k nown to participate to the process of neuronal differentiation, were associ ated with the sphingolipid-enriched domains in a way specific for the type of kinase and for the developmental stage of the cell. Proteins belonging t o other signaling pathways, such as phosphoinositide 3-kinase and its downs tream target, Akt, were not associated with the domains.