The expression and activity of SPHK1 are reduced in MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-induced murine model of PD (Fig. 5) [194], which can lead to enhanced ROS as well as BAX and HRK (harakiri) mRNA expression [205]. Here, HRK is linked to Parkinson disease.