Bipotential roles of ceramide in the growth of hippocampal neurons: promotion of cell survival and dendritic outgrowth in dose- and developmental stage-dependent manners.

Ceramide is now regarded as a lipid messenger molecule involved in a variety of cellular processes, including growth, differentiation, and cell death. Previously, we demonstrated that ceramide is required for cell survival and dendritic growth of cerebellar Purkinje neurons (Furuya et al.: J Neurochem 65: 1551-1561, 1995). Here, we show that ceramide plays growth-supportive roles in hippocampal neurons at immature stages of development. Application of cell-permeable N-hexanoyl-D-erythro-sphingosine (C6-ceramide) at a concentration of 3 microM promoted cell survival and dendritic outgrowth of the immature neurons. A structurally related compound, N-hexanoyl-D-erythro-dihydrosphingosine (C6-dihydroceramide), was ineffective, showing a requirement of 4-5 double bonds in the sphingosine moiety for activity. Incorporation of 5-bromo-2'-deoxyuridine into neurons was not altered by the treatment with C6-ceramide, indicating that C6-ceramide did not facilitate neuronal proliferation but protected hippocampal neurons against basal cell death. The survival-promoting activity of C6-ceramide, however, appeared to be biphasic; C6-ceramide at a concentration of 10 microM caused retraction of the dendrites and detachment of the neurons from the culture plate followed by cell death. In contrast to the immature neurons, the treatment of mature hippocampal neurons with C6-ceramide did not support cell survival but caused nonnecrotic cell death, even at a concentration of 3 microM. These results suggest strongly that ceramide regulates the fate of hippocampal neurons, depending on its concentration and on the developmental stage.