Abstract
Sphingolipids, particularly gangliosides, are enriched in neuronal membranes where they have been implicated as mediators of various regulatory events. We recently provided evidence that sphingolipid synthesis is necessary to maintain neuronal growth by demonstrating that in hippocampal neurons, inhibition of ceramide synthesis by Fumonisin B1 (FB1) disrupted axonal outgrowth (Harel, R. and Futerman, A. H. (1993) J. Biol. Chem. 268, 14476-14481). We now analyze further the relationship between neuronal growth and sphingolipid metabolism by examining the effect of an inhibitor of glucosylceramide synthesis, D-threo-1-phenyl-2-decanoylamino-3-morpholino-1- propanol (PDMP) and by examining the effects of both FB1 and PDMP at various stages of neuronal development. No effects of FB1 or PDMP were observed during the first 2 days in culture, but by day 3 axonal morphology was significantly altered, irrespective of the time of addition of the inhibitors to the cultures. Cells incubated with FB1 or PDMP had a shorter axon plexus and less axonal branches. FB1 appeared to cause a retraction of axonal branches between days 2 and 3, although long term incubation had no apparent effect on neuronal morphology or on the segregation of axonal or dendritic proteins. In contrast, incubation of neurons with conduritol B-epoxide, an inhibitor of glucosylceramide degradation, caused an increase in the number of axonal branches and a corresponding increase in the length of the axon plexus. A direct correlation was observed between the number of axonal branch points per cell and the extent of inhibition of either sphingolipid synthesis or degradation. These results suggest that sphingolipids play an important role in the formation or stabilization of axonal branches.
Highlights
conduritol B-epoxide (CBE) causes accumulation of GlcCer in a variety of cell types no effects on cell growth have been reported. We demonstrate that both Fumonisin BI (FBI) and PDMP reduce axonal growth in cultured hippocampal neurons by altering the ability of neurons to either form or stabilize axonal branches
We previously demonstrated that inhibition of ceramide (Cer) synthesis in hippocampal neurons by FBI reduced the length of the longest axon between days 2 and 3 in culture and that addition of Cer together with FBI reversed this effect [5]
To analyze further the role of SL metabolism in neuronal development, we have compared the effects of FBI with those of PDMP and CBE, inhibitors of GlcCer synthesis and degradation, respectively (Fig. 1)
Summary
INHIBITION OF SPHINGOLIPID SYNTHESIS AND DEGRADATION HAVE OPPOSITE EFFECTS ON AXONAL BRANCHING*. We recently demonstrated [5] that Fumonisin BI (FBI)' an inhibitor of dihydroceramide synthesis [12] (Fig. 1), disrupts axonal growth These results are consistent with experiments which suggest that SLs are essential for cell growth in Chinese hamster ovary cells [13]. In order to further elucidate the role of SLs in neuronal development, we compare the effect of FBI with that of I-phenyl-2-decanoylamino-3-morpholino-l-propanol (PDMP), an inhibitor of glucosylceramide (GlcCer) synthesis [14, 15] (Fig. 1). CBE has an opposite effect, causing an increase in axonal growth and branching These data suggest that SLs play an important role in axonal development, and imply that modulation of SL metabolism may provide a mechanism for regulating neuronal growth
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
