Figure 1.

Sphingosine-1-phosphate (S1P) reduces neurite outgrowth of adult dorsal root ganglia (DRG) neurons in vitro. (A) Representative examples of DRG neuron cultures from wild-type (wt) mice under the effect of S1P. Scale bar = 30 μm. Neurons were cultivated with or without S1P (1 μM) for 24 h and stained with Tuj-1. (B) Neurite length of 24 h cultured wt neurons was significantly decreased upon S1P treatment (596.4 ± 41.48 μm for ctrl vs. 318.4 ± 35.28 μm for S1P-treated, ***p < 0.001, U-test; ctrl n = 209, S1P n = 129). (C) The percentage of neurite bearing cells in treated cultures was significantly reduced compared to untreated cultures (42.88 ± 1.82% for ctrl vs. 19.33 ± 4.93% for S1P-treated, ***p = 0.000391, χ²-test; ctrl n = 209, S1P n = 129). (D) Treatment for 24 h with SphKs inhibitor ABC294640 (ABC) did not induce any significant effect on the total neurite length of either wt or Sphk1^−/− DRG neurons (n.s., Kruskal-Wallis test, p = 0.092; 1071.03 ± 85.33 μm for wt ABC and 1235.60 ± 89.79 μm for Sphk1^−/− ABC; wt vehicle n = 337, ABC n = 291; Sphk1^−/− vehicle n = 279, ABC n = 279).