Application of exogenous ceramide to cultured rat spinal motoneurons promotes survival or death by regulation of apoptosis depending on its concentrations

The membrane lipid ceramide (Cer) has been shown to be involved in the survival and dendritic growth of cerebellar Purkinje cells and hippocampal neurons. We examined the effects of Cer on isolated rat spinal motoneurons. Basal neuronal cell death due to Apoptosis occurs under these culture conditions. This cell death was prevented by treatment with 2.5 microM of D-erythro-N-hexsanoylsphingosine (C6-Cer), a cell-permeable analogue, and the surviving cell number was increased approximately 1.6-fold compared with the control cell number on 5 days in vitro (DIV). Application of the same amount of C6-Cer improved axonal elongation. Conversely, addition of 10 microM of C6-Cer led all motoneurons to apoptotic cell death by 2DIV. A stereo isomer, threo-C6-Cer, which is not metabolized to C6-glucosylceramide, also promoted survival, death, and axonal growth in the same manners as C6-Cer. However, C6-dihydro-Cer, a biologically inactive analogue, had no effects on survival or death, indicating that the presence of a double bond in the sphingosine base is essential for its activity. In addition, treatment with Bacterial sphingomyelinase, which generates endogenous Cer, increases motoneuron survival and axonal growth. These observations suggest that Cer, but not its metabolites, regulates survival and development of spinal motoneurons, depending on its intracellular concentration.