INDUCTION OF GANGLIOSIDE BIOSYNTHESIS AND NEURITE OUTGROWTH OF PRIMARY CULTURED NEURONS BY O-1-PHENYL-2-DECANOYLAMINO-3-MORPHOLINO-1-PROPANOL

We reported previously that stereoisomers of 1-phenyl-2-decanoylamino- 3-morpholino-1-propanol (PDMP),the D-threo and L-threo forms, exerted inhibitory and stimulatory effects on glycosphingolipid (GSL) biosynth esis in B16 melanoma cells, respectively. In the present study, the pr imary cultured rat neocortical explants were treated with L- or D-thre o-PDMP. These isomers exhibited opposite effects on neurite outgrowth: D-PDMP was inhibitory at concentrations ranging from 5 to 20 mu M, wh ereas L-PDMP was stimulatory over the same concentration range, and th e maximal effect was observed at 10-15 mu M. Rat neocortical explants were doubly labeled with [C-14]serine and [H-3]galactose at 15 mu M L- or D-PDMP. L-PDMP increased the incorporations of both labels into sp hinganine, sphingosine, ceramide, sphingomyelin, neutral GSLs, and gan gliosides, whereas D-PDMP inhibited the glucosylation of ceramide resu lting in a reduction of ganglioside biosynthesis and accumulation of p recursors of glucosylceramide, ceramide, and sphingomyelin. To clarify the stimulatory effect of L-PDMP on GSL biosynthesis, serine palmitoy ltransferase, sphingosine N-acyltransferase, glucosylceramide synthase , lactosylceramide synthase, GM3 synthase, and GD3 synthase were quant ified in cell lysates of explants pretreated with this agent. Serine p almitoyltransferase was fully activated up to 150% of the control. Fur thermore, marked increases in the activities of lactosylceramide synth ase (200%), GM3 synthase (240%), and GD3 synthase (300%) were observed . These results suggest that the neurotrophic action of L-PDMP may be ascribable to its stimulatory effect on the biosynthesis of GSLs, espe cially that of gangliosides.