Inhibition of sphingolipid synthesis affects kinetics but not fidelity of L1/NgCAM transport along direct but not transcytotic axonal pathways.
Glycosphingolipids are constituents of lipid rafts which might function in sorting apical and axonal cargoes in the trans-Golgi network. In fact, two GPI-linked proteins, Thy1 and PrPC, require lipid raft lipids for sorting to the axon. It was previously shown that inhibition of glycosphingolipid synthesis by FumonisinB1 (FB1) impairs axon outgrowth but not axon specification, leading to the hypothesis that formation of axonally-targeted vesicles is coupled to sphingolipid synthesis. Since the axonal cell adhesion molecule L1/NgCAM can partition into membrane rafts biochemically, we asked whether correct targeting to the axon is FB1-sensitive, similarly to GPI-linked proteins. We previously showed that cultured hippocampal neurons use more than one trafficking pathway to the axon: a transcytotic pathway and a direct pathway. We show here that reducing raft lipid levels does not disrupt axonal targeting of L1/NgCAM along either pathway. Unexpectedly, FB1 selectively slowed the kinetics of surface expression of a truncated NgCAM using the direct pathway, but not of NgCAM using the transcytotic pathway. Therefore, the formation and/or transport of a subset of axonally-targeted vesicles are coupled to sphingolipid synthesis. Our results yield a mechanism for the axon outgrowth defect observed in FB1.
Chang
Michael C
MC
Department of Neuroscience, University of Virginia, 409 Lane Road, MR4-6112, Charlottesville, VA 22908, USA.
Wisco
Dolora
D
Ewers
Helge
H
Norden
Caren
C
Winckler
Bettina
B
D000818:Animals; D001370:Axonal Transport / Q000502:physiology*; D001369:Axons / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D001921:Brain / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*; D051242:Caveolin 1 / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D003902:Detergents / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D037341:Fumonisins / Q000494:pharmacology; D005677:G(M1) Ganglioside / Q000378:metabolism; D020439:Growth Cones / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D006624:Hippocampus / Q000166:cytology / Q000254:growth & development / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D021962:Membrane Microdomains / Q000187:drug effects / Q000378:metabolism*; D039842:Neural Cell Adhesion Molecule L1 / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology; D051381:Rats; D013107:Sphingolipids / Q000096:biosynthesis*; D022161:Transport Vesicles / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure
D051242:Caveolin 1; D003902:Detergents; D004791:Enzyme Inhibitors; D037341:Fumonisins; D039842:Neural Cell Adhesion Molecule L1; D013107:Sphingolipids; D005677:G(M1) Ganglioside; C056933:fumonisin B1