S1PR1 and Parkinson disease: Accordingly, levels of SPHK2, S1P and S1P1 were reduced in the SN of a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD murine model16, and addition of exogenous S1P to 1-methyl-4-phenylpyridinium (MPP+)-treated dopaminergic neuron cultures was found to exert a neuroprotective effect16, 17, 18.